Do standard definitions exist for dragon, drake, wyrm and wyvern?

Question: In many different books including Dragonlance, Tales from the Sword Coast, Magic: The Gathering and other similar fantasy series, I've seen references to dragons, drakes, wyrms and wyvern (which may be plural version of wyrm?). Is there a standard definition of each; and if so, what are the differences between them?
From my readings, I understand dragons have different colors which designate their power, attitude, magical ability, alignment and so forth and that wyrms also have color but it is less significant.
Drakes are smaller than dragons, but still fly and breath fire but have no magical abilities. Basically, Drakes are evil.
Wyrm/wyverns are more snake-like and will live in caves and mountains protecting their loot. I've also heard references to dragons doing this as well, but only in movies where the naming is simply used for convenience.
Comment: The answer to your question as given is that there is no standard definition for the fantasy genre. Various mythologies have their own definitions, and different fantasy worlds have their own definitions and distinctions. If there's a particular canon you are interested in, that might make for a question with a more satisfying answer.
Comment: Magic: The Gathering famously has wurms, worms and wyrms.
Comment: @JohnO - I disagree and have voted accordingly. Asking what a dragon looks like in fiction and mythology is the textbook definition of too broad. Entire *shelves* of books have been written on the subject, let alone comparing them to the three dragon-like creatures mentioned.
Comment: @edlothiad - For the record, I also flagged this to be "Historically locked" given the obvious interest, even if it's now off-topic by current standards
Comment: @Valorum except it's not off-topic. It's on-topic. While not a list, your reasoning for too broad "lots of possible answers" is pretty well covered in this [well up-voted meta post](https://scifi.meta.stackexchange.com/q/1465/68872), which addresses the concerns of possible list questions and "Yes/No" answers. Can you provide any evidence from our policies that this is indeed off-topic?
Comment: @Edlothiad - Sure, if all you're looking at is the title then this is a straight yes/no question.
Comment: I do not believe this is too broad a question or deserves to be closed. An well-written answer that explains there is no difference (in the genre) and why this is so would be a good addition to this site.
Comment: [An article about this on DailyMTG](https://magic.wizards.com/en/articles/archive/drakes-and-dragons-wurms-and-worms-2007-11-14)
Comment: While that seems to be quite a harsh punishment that JohnO suggests, especially to someone who has dedicated so much time and effort to be improving this site, this question is certainly not too broad as the OP is asking a Yes/No question on whether standard definitions exist. This question should be reopened.
Answer: A lot of the material and references you mention are part of the Dungeons and Dragons game source material.
In particular, Tales of the Sword Coast takes place in the Forgotten Realms setting, which is a campaign world designed by Ed Greenwood for his Dungeons and Dragons game, and which eventually became a licensed product that included source books, novels, video games, and more.
Dragon Lance is another licensed Dungeons and Dragons campaign setting, that was somewhat modified from the main rule sets available at the time.
Magic the Gathering, however, takes its cues from its own source material, although it does borrow rather heavily from other genres and sources, including Dungeons and Dragons.
In the basic Dungeons and Dragons original rules, Dragons were at the top of the chain of the various "draconic monsters".  Each species of "true" dragon was identified by a basic color (red, blue, green, white, bronze, silver, gold), and had varying levels of intelligence, personality, and abilities (including the "breath weapon", which depended upon the color, and could be anything from fire to magical gas).  Later on, the types of dragons were expanded consisiderably, including things like "gem dragons", planar dragons, and undead dragons (dragon liches).  The size of dragons generally scales with age, with adults being quite large (dozens of feet from tail to snout on even moderate sized adults).
Some dragons are quite intelligent, surpassing that of most humans, while others are on the low end of the intelligence scale.
Dragons traditionally had a notable fondness for treasure.
Smaug, the dragon from Tolkien's The Hobbit, was undoubtedly one of the primary inspirations for the early Dungeons and Dragons dragon types.  However, later on there were other dragon types introduced more closely based upon eastern mythologies, or purely from the authors' imaginations.
Drakes are sometimes used to refer to immature dragons, but are more frequently associated with much smaller reptilian animals that are mostly just 'scaled down' versions of regular dragons.  Depending on the source, they may or may not be intelligent, and may or may not have the ability to breath fire.  Typically, they are large reptiles (from 2-3 feet in length up to much larger sizes, depending on the source) that can fly and have a generally "dragonlike" appearance.
Wyrm sometimes refers to the oldest and largest types of traditional dragons.  However, it can also refer to dragons that are specifically wingless.
Wyverns are quite separate.  They are normally depicted as smaller than a full-sized dragon, but still quite large.  They are winged and frequently have a barbed tail (sometimes poisonous).
However, as has been mentioned elsewhere, the terminology varies widely from source to source, and many of terms can easily be interpreted as interchangeable in many works.
** In traditional European heraldry, wyverns were typically depicted as dragon-like critters with only one pair of legs instead of two (or sometimes without legs at all).
Comment: Note that Smaug is also referred to as a "worm" in the Hobbit. Glaurung is called the Gold-worm of Angband, and there was also another wingless cold-dragon named Scatha the Worm. It appears that for Tolkien drake, wyrm, worm, serpent, and dragon were synonyms.
Comment: +1 For the detailed answer! Btw, isn't Smaug also referred to as "a fire-drake from the North"? At least in the movie? I don't think _The Hobbit_ made a difference between dragons and drakes.
Comment: Also, many types of wyverns tend to not have a set of front legs, just having the wings instead (like most birds).
Comment: The only glaring thing I see missing from this answer is the acknowledgement that sometimes they are all just words for the same thing. As Andres and horatio pointed out, in Middle Earth there is no difference. +1 if you add that acknowledgement.
Comment: also like to point out that Smaug was somewhat based off of the dragon from Beowulf
Comment: Just as an aside - In heraldry wyvern are four limbed (two arms, two legs) and dragons are six limbed (two arms, four legs).  Indeed an awful lot of "dragons or wyvern" in heraldry are actually neither - they are panthers - or more specifically - a panther incensed - and are often mistaken because they depicted breathing fire. e.g. https://en.wikipedia.org/wiki/Panther_(legendary_creature)#/media/File:RaglanPanther.gif
Comment: @AndresF. at first it is, but later on they refer to it as a dragon. That's what prompted my question actually.
Comment: @Mr.Mindor fair enough. I've made an edit.
Comment: Just as a side-note, in heraldry and in ancient lore traditions the wyverns with a barbed tail are sea-dwelling wyverns.
Answer: There is lore about Dragon-ish creatures across Eurpoe and Asia from which the inspiration for dragons in our favorite novels and games comes.  The words Dragon, Drake and Wyrm are all synonymous in terms of their etimology and historical definitions.  If you look at the etimology of words meaning dragon and the variety of lore about them, it is interesting to note in some cultures, sea serpents would be one in the same with dragons (particularly in Norse legend) and Biblical references may be referring to crocodiles or to the devil - depending on context, so historically speaking, a dragon is any kind of giant reptile with or without legs, wings, or fire-breathing ability (or the devil).
Wyrm is derived from an ancient germanic term.  Dragon from the roman draconem and/or Greek drakon (which both mean serpent) and Drake originates from the same drakon through the dutch word draak.  Wyvern is the same in essence that it comes from a Middle English word for snake, wyver and probably derives from the same latin root as the word viper.
Over time, traditions have changed things somewhat - in particular, how these creatures play out in heraldry.  Wyverns are a part of some family crests and hold up shields within those crests and are the only one of these four words with a distinct definition in a standard dictionary.  Because of heraldic rules, wyverns have been given a specific and distinct definition legally in England as of the 10th century.  Their specific and uniqe identity has become accepted and they are now considered to be a separate creature by most people that know the word, where as the other three are generally synonymous (unless otherwise defined within the particular story or game in which they appear).  Wyverns have two smallish wings and only have two short legs (that are more like a bird of prey's than lizard-like, where-as in Western European Tradition Dragons have larger bodies and wings and four legs (and that is how you tell them apart).  There is a sea-dwelling wyvern that has a thicker tail that is also barbed as well as a land-dwelling wyvern that does not usually have a barbed tail.  I think today the barbed tail is showing up more often (though the one on my family crest is not barbed).
Norse dragons tend to be more like great sea snakes and are much more serpenty those in the British Isles and France might think about.  In most fantasy novels dragons such as these would be described as being sea serpents (notibly Cressida Cowell's How to Train your dragon included "Sea-serpent" dragons as well as those more like Welsh and English dragons).
Chinese dragons also very rarely have wings (Yinglong is the most notable exception), but although their bodies are serpent like, they have talons like a bird of prey, whiskers adn sometimes deer like horns or antlers.  Even though they don't have wings they are able to ride clouds and water spouts into the heavens, so they still "fly."  They are a symbol of power and are often associated with the emporer.
It is the Chinese dragon that is traditionally classified by color and may be the inspiration for this element within D and D and any other "world" in which you have encountered color classifications.
In China, Black dragons are a symbol of the north and are portents of storms while red Dragons symbolize the west, pleasures and summer (in England, Red Dragons are a symbol of royalty) Back in China, white dragons symbolize the south and are associated with death and famine while blue dragons are associated with the spring and are a symbol of the east.  Finally, yellow dragons are supposed to bring the prayers of the people to the gods so they are the most secluded and not associated with a compass direction.  Yellow dragons can also symbolize scholarliness and supposedly brought the skill of writing to earth and taught it to the people.  Chinese also traditionally can classify their dragons by "jobs" or "responsibilities" of the dragons.  These classifications are ones I am less familiar with and their are significantly more of them.
When reading fantasy, usually the dragons described hearken to either a British/French/Ancient Roman Model of some sort, or, less often, in western literature, a more chinese form of the dragon depending on the story and the author's design.  Once in awhile you might get some unique variations based on the ancient greek versions such as Python (a monstrous serpent with the head and breasts of a woman) or the wingless Persian version of a dragon, but they are still defined by the author creating the particular world about which you are reading.  Many good authors will find a piece of something they find in the ancient lore about dragons and make it work within their story for them.  One author might be inspired by the color classifications in Chinese, but like the look of a Welsh dragon better for their puposes, so they'll mix the two ideas to create dragons and a set of dragon rules that work well for the world he/she has created.
Happy reading!
Comment: +1, this deals much more with the question as written than the accepted answer.
Answer: There's not a standard definition across the fantasy genre.
Sometimes they are different things, sometimes they are subsets of each other (e.g. a drake is a young dragon or a wyrm is a dragon with no legs). Sometimes they are even more diverse -- in the Warcraft canon, for example, wyverns appear as some sort of wolfy lion thing with bat wings and a scorpion tail.
There are some general definitions from mythology which probably fall under general reference -- you can find them in wikipedia or a dictionary. In fantasy fiction they vary wildly from canon to canon.
Comment: The World of Warcraft wyvern is what is more commonly referred to as a [manticore](https://en.wikipedia.org/wiki/Manticore) outside of that particular setting.
Answer: I have researched this topic quite extensively. Here are my conclusions.
Drake: Can be used synonymously to the word "Dragon", but in reference to a specific type of dragon, it is any four-legged wingless dragon. Obviously, there can be lots of variations of this, but this is just a standard definition.
sources: https://dragons.fandom.com/wiki/Drake and http://www.blackdrago.com/types.htm
Wyrm: A giant serpent, usually dwells in swamps or rivers. They usually have a dragon-like head.
sources: https://dragons.fandom.com/wiki/Wyrm and http://www.blackdrago.com/types/wurm.htm
Wyvern: A winged dragon with only two legs and a barbed tail. They are usually less intelligent than a standard Western Dragon.
sources: https://dragons.fandom.com/wiki/Wyvern and
http://www.blackdrago.com/types/wyvern.htm
But the thing to remember is that in a work of literature or another form of fiction the author is the deciding factor of exactly what the definitions are. And everyone has their own interpretation of what a dragon is.
Comment: Just an additional note; fandom.com sites are fan-written, so it's usually better to directly cite _their_ sources, assuming they are as clear-cut as that.
Comment: Note that you can format links like [link text] (link) (without the space) instead of leaving them bare so they're more readable.
Comment: That's why I sourced two fandoms so that I'm getting multiple sets of info and then using the overlap
Answer: Typically, and this is not a hard and fast rule as different societies and storytellers will define things differently...

Dragons are your prototypical beasts with four legs and wings. Whether they can use magic or  depends on the story being told.
Drakes are a little tough. Often, they are similar to the standard "dragon" with the difference that they typically do not have wings. These are often also referred to as Eastern Dragons or Chinese Dragon. In other instances, Drake is synonymous with Wyrm.
Wyrms (also known as European Dragons) and Wyverns (also knwn  are typically identified by the fact that they only have two legs at maximum. Wyrms are often depicted as being more serpent-like than Wyverns. Wyverns will sometimes have no legs at all.
Comment: Like I said in Beofett's answer, in _The Hobbit_, Smaug is mentioned as being a "fire-drake" as well as a dragon. And he is definitely a Western-style dragon, with wings and four legs :)
Comment: Yes, and that's the problem with things like rules and definitions for dragons or zombies or whatever: there are no hard and fast rules. What one author or even culture decides has little to no bearing on what the next does.
Answer: I believe that wyrm is just an interchangeable name for a dragon, used most notably in the Dungeons and Dragons setting as a stage of a dragon's life.
Wyverns are similar to but separate creatures from dragons, having only four limbs (two legs, two wings) and being unable to breathe fire.
I'm not sure about drakes. In the Hobbit, Smaug was mentioned as being "a fire-drake from the North", but also a dragon, which implies that the two have basically the same meaning.
Answer: From what I have played, read, and watched there are 6 types of typical fantasy species in the draconian family. What I am writing is talking about their physical attributes and not their powers or abilities.
Dragon: Has 4 legs, 2 wings, and one tail
Wyvern: Has 2 legs, 2 wings/arms, and one tail
Drake: Has 4 legs, no wings, and one tail
Wyrm: no arms/legs and up to several tails
Lindwyrm: 2 legs and a tail like a wyrm
Amphiptere: no legs/arms and tail like wyrm, but with 2 wings
I know this isn't the best listing of all the differences but this is just an overall aspect and not definite details.
Comment: Hi, welcome to SF&F.  What is this list based on?  If these are standard definitions you should be able to cite at least one source for each.
Answer: I have seen usage in Norse Mythos (Note I am talking not of Norse Pagan belief but of the tales told by Norsemen, which would be garnered from all manners of cultures through stories told by travellers.)
Wyrm was used to describe huge serpents, all legless, but possibly winged, tjat were essentially plague incarnate. Their mouths drooled saliva that made living forests rot, and would turn a mans innards to soup.
Worm described any non-elementally attributed large serpent. The Midgard Serpent is a giant fish serpent and could be classified as a worm in most cases due to lack of any sort of magical abilities, besides it being large enough to wrap around the world.
Wyverns are highly varied, and were named as lindworms by the norse. Some tales speak of bird sized lizards with wings and poisonous barbed tails, whilst others describe what most consider to be drakes. The common features of all wyverns are:
Feathers,
Cunning,
Forked Toungues,
and Large, raptor-like (as described a raptors claw comes to mind; they obviously did not mention raptors by name) claws.
Drakes are usually between the size of a small pony to the size of four oxen or yak. They are two legged dragons that are much less intelligent, but flock around their larger cousins as scavengers.
Dragons are usually four legged, around the size of a small home to that of a chapel. They can breath fire, or boiling mists, and some rare cases had breath of ice. They were malevolent beasts, almost as smart as man, who had specific greeds. Some were gluttonous, some were hoarders of treasures, and others were perverts (this last category seems to stem from bawdy tavern tales ;). They were nigh on impossible to kill, and had varying ranges of magical powers, from shapeshifting, to telepathy, to the ability to make nature do their bidding.  most tales end either with a dragon sleeping off its last meal, or getting beheaded by a strong, male hero.
Evern more classifications exist but almost all have overlapping terms, and thereofre I shall not go into further detail.
Answer: OK, I got this one. First things first, in mythology, dragon refers to the species as a whole, with most names just referring to the breed. Also, most dragons (and wyrms) are sentient and highly intelligent.
A drake is your typical European dragon, with four legs and two wings, and are known for storing and guarding items they deem as valuable. Drakes are usually hostile, though there are exceptions. Certain variants of drakes breath different substances, though the colour does not determine this in most circumstances. What you thought was a drake, is actually a dragonette, which is a much smaller variant of drake with varying demeanour and elements, though most dragonettes use venom as their main method of protection.
A wyrm is a separate being altogether, that are similar to dragons but are not the same. There are two variants of wyrm, the airborne and the landborne. The airborne's are wyrms that lack wings, similar to a loong (Chinese Dragon), and also lack legs. They spend most of their time flying around, rarely ever landing, though they can land. Upon landing, they pretty much are just a giant snake with horns. The landbornes are an anthropomorphic variant, that is bipedal with shorter arms. They do have wings, but they don't fly often, with running being their most effective method of transportation.
Wyverns are dragons that have large wings, longer bodies, and commonly only two legs, however, elder wyverns have four legs. Wyverns tend to have crocodile-like heads and are only hostile if threatened. A wyvern spends it's time mainly in the air, but lands to eat, rest or have... Questionable wrestling sessions with their mates.
Answer: Just to clarify in terms of the Wyvern,
A Wyvern is very similar to a dragon but usually smaller and they only have two legs and two wings, whereas a Dragon usually has four legs and two wings
Comment: Hi Patrick. Your clarification should probably be a comment in the main question, since it doesn't actually attempt to answer it :)
Answer: What I've concluded from reading several books and more importantly, asking for detailed information from a couple of RPing and Dragonic lore forums;
Dragons,
Dragons are great variations of reptilian species with SIX appendages; four legs and two wings. They have a great variation of colour and shape(Read: Horns, claws, and skin) depending on habitat they live in. Depending on lore they may or may not be capable of breathing fire and/or other substances by means of magic or plain scientific reactions. Also notable is that dragons are often portrayed as either intelligent to the point of being sapient, or to the point of far outmatching other animals.
Drakes,
Drakes as far as I've concluded are WINGLESS dragons(Which others above me have denied), smaller in size and less intelligent, albeit far from dumb. They also have a notably smoother skin and less colour variation. Crudely explained they're big, reptilian dogs.
Wyverns,
Wyverns are older variations of dragons, to the point of having less appendages(That is, the  front pair of legs doubles as wings, sometimes with claws on the elbow), less intelligence, and inferior instincts. Most likely so because they're less evolved versions of dragons.
Wyrms,
Wyrms are the most ancient version of dragons, most likely the whole race of dragons decended from this particular species. They cover a considerably bigger span of time than the previous three apparitions combined, explaining why their appearance ranges from giant worms to wormish-dragons. Wyrms are, as stated priorly, giant worms, with reptilian skin, and bigger, cruder faces, the eldest versions of wyrms don't even have horns. Wyrms are known for living underground. Later on they evolved wings and became sleeker in form; Chinese dragons are wyrms halfway trough evolving to Wyverns.
The evolutionary tree of these species goes like this:
Wyrms -> Wyverns -> Dragons + Drakes
As you can see, drakes and dragons are familiars trough the wyvern, they have both evolved differently, explained by the evolutionary theory of Charles Darwin(Due to living in a different ecosystem, Drakes didn't have the need to either fly or breath fire).
So, there you have it, the history of draconic beings as far as I can conclude from different sources
Comment: Can you site sources? I've yet to see a drake without wings.
Answer: <code>               **The Difference Between Dragons, Drakes, Wyrms and Wyverns**
</code>
Size and Shape
Dragons are larger than drakes, but smaller than wyverns.
Dragons have a longer body and throat than drakes.
Wyverns are four-limb creatures (one pair of legs and one pair of wings), drakes are six-limb creatures just like the dragon (one pair of wings and two pair of legs).
Wyrms are very snake-like creatures that has six limbs (a very flexible body and occasionally a pair of wings or legs). Wyrms are very slim when conferring to dragons, drakes and wyverns, but they are also very long.
Abilities
Dragons are renowned for breathing fire and various magical abilities, but drakes can breath fire to, also wyverns and wyrms can spit fire. Drakes doesn't have any magical abilities (except breathing fire).
Comment: Can you cite any references?
Answer: As I've always understood it. The drake, dragon and wyrm were ages of dragons. Wyvern is a different creature altogether, albiet similar, it lacks 2 legs. A Drake is a young dragon...a juvenile, Dragon is used when speaking about an adult and Wyrm is an elder, one that has acquired great age and power... the eldest often referred to as "great wyrm"
Comment: I doubt this is correct. Keep in mind the answer must be universal for Dragonlance, Magic: The Gatheric, and  "similar fantasy series". I don't think in general fantasy fiction Wyrms are "elder dragons", for example.


Win32::API fail to load win32 dll

Question: I am trying to use a Win32 dll in a perl script using Win32::API module.
For this I have written a perl script like this
use Win32::API;
$Win32::API::DEBUG = 1;
$function = Win32::API->new(
  'mydll.dll', 'int func()',
);
$return = $function->Call();

But I am getting the following error:
Win32::API::new: Loading library 'mydll.dll'
FAILED Loading library 'mydll.dll': The specified module could not be found.
Can't call method "Call" on an undefined value at .\test_dll.pl line 6.

Although the script and the dll are at the same location, so there is no way it can't find the dll. Also i have tried using the full path.
I am using active perl 5.16 on Windos 7 platform. I have tried this with 5.14 too without any help
What is happening here?
Answer: This is resolved after adding the other dependent dlls to  the same place as it is .

Win32::API fail to load win32 dll


How to explicitly see the ramification over infinity

Question: Take the equation $y^{d}=\Pi_{1}^{n}(x-t_{i})^{m_{i}}$ over $\mathbb{C}$. This affine equation gives a cyclic cover of $\mathbb{P}^{1}$. Now it is usually said without explanation that if the sum $\sum m_{i}$ is not divisible by $d$, then the family is ramified over $\infty$. My question is how to see explicitly--in terms of equations maybe--that this is the case.
Comment: Consider analytic continuation of the function `$\sqrt[d]\prod_1^n(z-t_i)^{m_i}$` along the circle $\{|z|=R\}$, $R\gg0$. How many different branches do you obtain?
Answer: Another way to do it is to compute explicitly the curve above the point at infinity, just by looking at the equation. The argument works over any field, we can of course assume that this one is algebraically closed.
The curve $y^d=\prod_{i=1}^n (x-t_i)^{m_i}$ is affine, and covers the affine line which coordinate is $x$. If you want to see what happens at infinity, you just change coordinates on $\mathbb{P}^1$, which corresponds to take affine coordinate $X=1/x$.
Assume that each $t_i$ is not equal to zero (otherwise, make an affine change of coordinates at begin). We then have
$\prod_{i=1}^n (x-t_i)^{m_i}=\frac{\prod_{i=1}^n (1/t_i-1/x)^{m_i}}{\prod_{i=1}^n (xt_i)^{m_i}}$.
(a) If $\sum m_i$ is a multiple of $d$, you write $\sum m_i=ad$ and make a change of variables $Y=yx^a$ and get
$(\prod_{i=1}^n t_i^{m_i} )Y^d=\prod_{i=1}^n (1/t_i-X)^{m_i}$
In this case, the curve is not ramified at infinity, which is $X=0$.
(b) If $\sum m_i$ is not a multiple of $d$, you write $\sum m_i=ad-k$ where $1\le k< d$ and make a change of variables $Y=yx^a$ and get
$(\prod_{i=1}^n t_i^{m_i} )Y^d=X^k\prod_{i=1}^n (1/t_i-X)^{m_i}$
In this case, the curve is ramified at infinity.
Answer: One way to see this is the following. Let $U$ be the complement of the points $t_1,\ldots,t_n$ in $\mathbb{P}^1(\mathbb{C})$. The fundamental group $\pi_1(U)$ is generated by elements $\gamma_1,\ldots,\gamma_n,\gamma_\infty$ with relation
$\gamma_\infty^{-1} = \gamma_1\cdots \gamma_n$. Consider the character
$\chi:\pi_1(U)\to \mathbb{C}^*$ defined by
$\chi(\gamma_i) = e^{2\pi m_i/d}, i = 1,\ldots,n$,
$\chi(\gamma_\infty) = e^{-2\pi M/d}$, where $M = \sum m_i$. Let $V$ be the quotient of the universal cover of $U$ by the kernel of $\chi$.
The normalization of your curve is isomorphic to the normalization of $\mathbb{P}^1$ in $V$. It is a smooth complete curve on which the cyclic group of order $d$ acts as the Galois group with quotient $\mathbb{P}^1$. The ramification over $\infty$ is defined by the value of $\chi$ at $\gamma_\infty$, i.e. $e^{2\pi M/d}$. It is trivial, and hence the cover is unramified over $\infty$ if and only if $d|M$. The ramification index is equal M\mod d.$
Comment: @DariusMath I believe user37622 meant to remove $t_1,\ldots,t_n$ from $\mathbb{C}$ itself, instead of the projective line.  We assume from the beginning that $\gamma_\infty$ appears.
Comment: Thanks for the argument. But isn't it that if you remove $n$ points of $\mathbb{P}^{1}$, the fundamental group is generated by $\gamma_{1}$,...,$\gamma_{n}$ with $\gamma_{1}...\gamma_{n}=1$? and of course we can't assume from the beginning that $\infty$ is a removed (i.e. branch point). So does $\gamma_{\infty}$ always appear?
Comment: Ah, OK. If we remove the points form $\mathbb{C}$ (i.e. remove the points together with $\infty$ from $\mathbb{P}^{1}$) then the argument will be correct. Thanks!


Can we use CAPITAL LETTERS to indicate actions?

Question: While designing for the web or the mobile applications, a natural free flowing text can be used for the general content, but when it comes to actions... can we use CAPITAL LETTERS.
Comment: SURE. GO RIGHT AHEAD.
Answer: As a general rule of typography using all caps reduces readability for long segments of text. It should never be used for paragraphs especially, and only for short headlines.
You can certainly use all caps in buttons, though, because buttons by nature contain short segments of text. In fact, all caps is the convention for buttons in Google's Material Design. You can see how they specify this at https://www.google.com/design/spec/components/buttons.html#
One thing I notice Google doesn't do is increase the letter-spacing when using all caps. In general it increases readability to add some spacing between all cap letters. See http://practicaltypography.com/all-caps.html
Answer: I don't see why not to use capital letters for buttons and actions. It can be quite nice and add visual discernment to your app. It would be wise to watch for device visual standards (e.g. Android Material and iOS have different visual standards).
You should also take care to make enough of white space around text to make it more clear and readable.
This is one example of readable button in web app:
Answer: There is nothing to stop you using capital letters (all-caps) to indicate actions. It should be noted, however, that there is no common pattern for all-caps indicating actions.
If you are using the pattern across your system then you will be encouraging your users to understand that, wherever they see all-caps within your system, there is an action available to them.
In short, other than basic readability,  there is no real issue with using or not using all-caps to indicate actions.
The only thing I would say in caution is that you may find this limiting when it comes to formatting other text that may require all-caps but is not an action.
Answer: How about use Small caps (https://en.wikipedia.org/wiki/Small_caps)? I guess Visual designer needs to look at it to be sure it will look ok. But its nice idea for button label (especially when you using serif fonts).
Comment: OK, that's an option. But why do you suggest it?
Comment: There's nothing wrong with using small caps in this situation, but it'd merely be an aesthetic decision. Small caps are designed to be used *with* lowercase letters. In other words, they're meant for the context of being used within a block of text.
Comment: @DA01 I suggest that more as visual design case As I mentioned - to avoid typical full caps screaming. Also I agree with Lea - button as itself provides a lot of opportunities to make it visible without using caps.
Answer: I really don't recommend you to use capitals for this case. For two reasons : capitals are less readable than smal cast and it's like if you were SPEAKING LOUDLY to your users.
There are many beautiful and efficient ways to highlight your content elements like a call to action without using capitals.
Comment: Context is important here. All-caps is certainly seen as SHOUTING ONLINE IN FORUMS AND THE LIKE but in the context of a button, not so much.


What's the disadvantage of ARMA-GARCH model?

Question: I want to ask why ARMA-GARCH is more and more popolar, and what's the advantage of this model.
Comment: The title is about _the_ (only one?) disadvantage while the question is about _the_ (again only one?) advantage?!?
Answer: You would use GARCH to account for stochastic volatility in a time series of returns. However, the returns time series may have components other than that can be explained by stochastic vol, such as trends or moving average. Therefore, ARMA or AR or some such series is used to de-trend. In risk managment it can be used for back testing, calculating VaR or ES. A good reference for this is Filtered Historical Simulation by Barone-Adesi(2000). Link for FHS. Also Kevin Dowd has good chapter explaining this - "Measuring Market Risk 2nd Ed, Chapter 4" -link Dowd.


Is it ok and useful to keep a security audit report after completing an audit?

Question: I recently ran a couple of security audits for some friends, and was thinking about doing some more. Before I do though, I wanted to know whether I should keep the audit reports and, if so, how? I understand that it's insecure to keep it, but at the same time, what happens if the client loses the files/report and needs new copies?
Comment: We can't answer the legal question
Answer: It depends on what your friends agreed to.
The fact that you did an audit for them implies that they are alright with you gaining knowledge of their system. Wether or not you are allowed to store that knowledge in some way for a prolonged period of time is something they must agree to explicitly.
You can state how you store the data (e.g. in an encrypted format, with the encryption key escrowed to a trusted third party, perhaps), and how you intend to use it.
However, keep in mind that I am not a lawyer, and if in doubt, you should always consult a lawyer for legal questions. They are much better equipped to talk about the laws in your specific region.
Why would you want to keep the audit report
As for usefulness, it certainly does have its uses. Most importantly, it gives you a quick overview over flaws you have found previously. This allows you to check if these specific flaws have been fixed since the last audit, or if there is still room for improvement.
It can also aid as a guide to see if your customer is heading in the right direction, or if they favor functionality over security - in which case you can definitely add to the audit that things had gotten worse since the last audit.
Keeping the audit in case the customer loses it is not really a valid use-case. Once you sent the customer the audit and they are happy with it, you did your job. It's up to them to keep their files safe, so if they lose it, it's not really your responsibility to provide them a copy. It's similar to how it's not the fault of the grocery store if you drop something in the parking lot and break it. (Of course, it's not unwise to provide them with a copy if they ask for it, but it shouldn't be your primary concern.)
Comment: I don't know that I agree that the customer must explicitly agree to the auditor keeping the audit.  Laws vary across the world, and I wouldn't assume either case.
Comment: @SteveSether Yes, it's entirely plausible that things are different in the US. At least here, you need to consent to such data being stored.


How to send a magic packet from OS X in order to wake a PC on the LAN? (WOL)

Question: Either some (preferably free/OS) app or a command line tool will do.
Answer: Install the wakeonlan package using Homebrew:
$ brew install wakeonlan
(It's a Perl script for waking up computers via Wake-On-LAN magic packets.)
When installed, you can send a "magic packet" from your Terminal to any device using its IP (Internet Protocol) and MAC (Media Access Control) address.
Here's an example of a typical use:
$ wakeonlan -i 192.168.1.255 -p 1234 01:02:03:04:05:06
The scripts takes 2 arguments, the MAC address of the NIC, and an IP address.

Note: The IP address argument is tricky and isn't what you'd think.
For a NIC on your local subnet, use the broadcast-address of this subnet. (e.g. subnet 192.168.10.0 with netmask 255.255.255.0, use 192.168.10.255)

For example, I have a Synology NAS manually configured with the IP address of 10.0.1.100 with a subnet mask of 255.255.255.0 and a router address of 10.0.1.1.
The correct IP address to use is not that of the device, but instead the broadcast-address of the subnet.
Continuing on my example, I used the following command to successfully wake up my Synology:
$ wakeonlan -i 10.0.1.255 -p 7 01:02:03:04:05:06
(Naturally, substitute the actual values of your device and network for your situation.)
You can get more information from the wakeonlan man page, man makeonlan, or a quick glossary of commands from wakeonlan -h.
Comment: Just a slight hint: looks like the command has three parameters, for -i the broadcast address (not the IP address), for -p the magic packet (which you do not explain, looks like you are showing 1234 or 7 as magic packet) and third parameter is the Ethernet (or MAC-) address.
Comment: @pebwindkraft , `-p` sets the destination port, actually (and defaults to 9).
Comment: FWIW, straight out of the box this worked for me to wake an Intel NUC using just `wakeonlan 94:c6:91:a1:68:22`. No parameters necessary. To be fair, the NUC is on my home LAN and I got the MAC address by running `arp -a` and recognising the IP address, so obviously the ARP table was still valid.
Comment: Like @HeathRaftery, I experienced the same — no need for any extra parameters. It actually makes some sense: on most LANs, you just need to broadcast on the segment where you are. The only reason for having this extra `-i` option is if you've got a router or bridge or similar multi-networked device, and have to specify in advance _which_ device/network to use...
Answer: Try WakeOnLan or wol — both are open source, both are available through MacPorts (and possibly through Homebrew as well).
Comment: WakeOnLan appears to no longer be available - the readpixel.com site linked above is being flagged as malware by Chrome, and it was also recently removed from homebrew-cask - https://github.com/Homebrew/homebrew-cask/issues/104849. I'd recommend using the open-source perl script from the homebrew formula in the answer below.
Answer: install:
# create a binary dir (-p, avoids error if dir exists)
mkdir -p $HOME/bin

# download the script
curl https://raw.githubusercontent.com/jpoliv/wakeonlan/master/wakeonlan -o ~/bin/wakeonlan
# give execution permission

chmod +x ~/bin/wakeonlan

wake:
~/bin/wakeonlan THE_MAC_ADDRESS

Comment: Could you expand your answer to explain what these commands do?
Comment: mkdir: make ad new directory; curl: Download "wakeonlan"; ~/bin/wakeonlan: execute the downloaded script.


Float doesn't work Yamaha Vino

Question: I recently wrecked my Yamaha vino and while I'm trying to replace some parts I thought I would fix the fuel gauge (which hasn't worked since I got the scooter a year ago.) I took the sensor out to test if it floats in water and it does but, when I put it back in the tank the float sinks right to the bottom. I tried it again today and the gauge still reads zero and it doesn't float. If I manipulate the floating arm the gauge will change appropriately. Any help would be nice and I'm always willing to answer questions!
Comment: Welcome to Motor Vehicle Maintenance & Repair!
Answer: You stated  you tested the float in water. The problem with your testing method is, water is heavier than gasoline. This means the float could be buoyant enough in water, but not in gasoline. I'd suggest your float is bad. In most cases, you have to replace the entire sending unit, which includes the float, not just the float itself.
Comment: They have a sink now, not a float!

Float doesn’t work Yamaha Vino


Wireshark filtering-trying to filter out my own local ip

Question: I'm trying to filter out my local machine's IP address 192.168.5.22.
I used ip.src != 192.168.5.22|| ip.dst !=192.168.5.22 and I keep seeing my address pop up.
Answer: Mitch is right. With the negative match like you have, you need both conditions to be true to filter off your IP, thus and instead of or.  You could also write it like so:
not (ip.addr == 192.168.5.22)

It might seem more logical to write it as ip.addr != 192.168.5.22, but while that's a valid expression, it will match the other end of the connection as not being the specific ip and still be true. For example, when connecting to 192.168.5.254 from 192.168.5.22, ip.addr != 192.168.5.22 doesn't match *.22 IP, it matches *.254 and thus the packet matches the filter expression. Here's a complete example to filter http as well:
not ip.addr == 192.168.5.22 and not tcp.dstport == 80

tcp.dstport != 80 suffers from a similar problem; having tcp.dstport != 80 turns out to mean "match ONLY tcp traffic, but only tcp that is not dstport == 80"
While not strictly your question, I prefer to do filtering in the capture filter (double click the interface name in the capture-options dialog), whose syntax is exactly like tcpdump. It makes the capture take less memory and disk by avoiding capturing packets you're telling it to ignore. The downside is those packets are not captured if you later want to inspect them and you can't change the filter selected this way during a capture session. For example, to keep from capturing http and ssh traffic to/from any host and any packets to or from 192.168.5.22,
not host 192.168.5.22 and not port 80 and not port 22

If you only wanted to filter http traffic to and from that host, you could do this:
not (host 192.168.5.22 and port 80)

Answer: Your or should be an and
ip.src != 18.104.22.168 && ip.dst != 220.127.116.11

Comment: That won't work. You need to `!ip.src == 18.104.22.168 ....`. Further `!ip.addr == 22.214.171.124` covers either.
Comment: @Scruffy, the answer is correct, this statement will filter out each fulfilled operator.
Answer: It's 2022 and IPv6 is now a thing! IPv6 makes this trickier since you'll usually have multiple v6 addresses and they often change.  Enumerating each is a pain. Instead we know that the link-local IPv6 prefix is FE80::/10 so to exclude traffic that both originates from and is destined to this range we use this filter:
not (ipv6.dst == fe80::/10 and ipv6.src == fe80::/10))
Putting it all together, this filter will exclude local IP, IPv6, and broadcast/multicast packets:
not (ipv6.dst == fe80::/10 and ipv6.src == fe80::/10) and
not (ip.dst == 192.168.0.0/16 and ip.src == 192.168.0.0/16) and
not (ip.dst == 10.0.0.0/8 and ip.src==10.0.0.0/8) and
not (eth.dst[0] & 1)

Note that the above only excludes local IP traffic in the 192.168.* and 10.* IP range.  There are other local ranges you might be using.  The and not (eth.dst[0] & 1) excludes any packet with the ethernet multicast bit set to true. If you want to see multicast traffic just exclude it. (it might also be better to just exclude multicast protocols, like with not mdns)


can I concatenate field values form a related list into a formula field?

Question: I want to ba able to concatenate the values of a field of a related list records into a field on the parent. How can I do this?
Comment: Keep an eye out on Declarative Lookup Rollup Summaries, specifically this https://github.com/afawcett/declarative-lookup-rollup-summaries/issues/76  for a clicks not code solution (free)
Answer: The only way to do this is with a trigger that does the concatenation when the child record is inserted, updated, or deleted.  This is a very costly trigger to write and you should proceed with caution taking into account the number of records you may be dealing with.
As far as I'm aware there is no "point-and-click" solution to this.
Comment: Bradley, Is there an example trigger somewhere that I could manipulate to achieve this task?
Comment: Hey Nicole, I would have to understand your use case. There's a lot of solutions to the issue that would produce very different trigger samples.  On another note, if you're asking the question in the first place, chances are there's a data model problem or some other solution to your problem.
Answer: No, you can't do this with a formula. Formulas can only do cross-object references to parent objects, not to child/related list records. The reason is that formulas only support referencing to a single record, and a related list potentially (usually) contain multiple records.
As @Bradley points out, you would require a trigger.
Comment: does a formula allow SUM of children (related) records?
Comment: No -- formula fields can only reference parent objects. Roll-up summary fields allow a SUM of child records, but are only available for master-detail relationships. (There are some AppExchange apps that allow you to get this functionality on lookup fields as well -- see my response in this post: http://salesforce.stackexchange.com/a/57086/2730 )
Answer: Maybe voting for this idea could help:

Ability to concatenate field values from related list
I want to be able to concatenate the values of a field in related list, i.e., child records. For example, If I have an account object and a contact reocrd. there is a one to many relationship between the two (one account, many contacts). The child record has a text field "second choice", I want to be able to show on each account record a field that concatenates all the "second choices" for all the contacts associated to the parent.


is there a way to prevent my pocket door from rubbing where the door handle goes?

Question: I was attempting to reuse a door when I installed my pocket door for my bathroom. As I installed the handle, I noticed the door is rubbing in the middle of the jamb. Where my guides are at the bottom, there is ample space, same as the top, middle, definitely leaning towards one side more than the other. Will/should I just replace the door?
Comment: Possible to pad the frame with something like felt furniture floor protectors. This could move door pathway enough
Comment: Are you saying that the door or the jamb (I assume you're referring to the opening into the pocket) is warped, or are both straight and they just don't hang quite right? You can check for warping with string or thread. Hold or tape the string to the middle of the door's edge at the top, then pull it taut and align to the middle at the bottom of the door's edge. If the string isn't in the middle of the edge halfway up the door then the door is warped. You can do something similar to check the opening of the pocket.
Answer: Use a straight edge, your eye, or a string to see what is warped. If the door is warped, then fine, replace it. But I doubt that the door is warped. It is much more likely that the wall is warped.
Unlike the door which has this and that engineered into it to keep it flat, there is nothing in a 2x4 to keep in flat. All lumber is crooked and most likely the wall builder forgot to crown the 2x4s away from the door so that the gap in the middle would be larger than the gap on the top and the bottom.
Do check just in case it is the door that is crooked. Also the hangers on the door usually allow to horizontal positioning. Play with that to send the door toward one side and see if you can stop it from rubbing.
Otherwise.... Oops. Time to cut the 2x4 out of the wall, flip it around, and reinstall.


Could hedges help in reducing noise?

Question: We live on a busy street with sound of tires and revving engines. We were wondering if hedges could help reduce the sound that comes into the house? if not, what other alternatives can we try? We already got soundproof curtains but it's still loud. Below is a photo of the front yard and the house.
Comment: I think that since the road is so low, that a hedge would visibly block traffic from most of the front windows. If that's the case, they will also dampen sound. The dampening is a factor of mu and the frequency, so it would work better on tire noise than engine noise. I would expect 2-3DBs of loss from a thick hedge, much more when it's covered in snow (if you choose an evergreen). Replacing the iron fence with wood could give you several more DBs. It will never be quieter than what you hear in the backyard though, be realistic.
Answer: A hedge can't reliably decrease the sound pressure level by more than 2 dBA (i.e. barely perceptible), and most of the reduction is in the higher frequencies (i.e. tire noise but not engine noise). This phenomena is well researched:

In the three trials where a significant attenuation of the noise occurred, the porosity of hedges measured less than 4.6% and an average noise reduction of about 2.7 dB(A) (max 7.0 dB(A)) was observed. This effect was particularly relevant in the range of higher frequencies (between 2 and 20 kHz).

Biocca, M., Gallo, P., Di Loreto, G., Imperi, G., Pochi, D., & Fornaciari, L. (2019). Noise attenuation provided by hedges. Journal of Agricultural Engineering, 50(3), 113-119.

Thick dense hedges are found to provide only a small total A-weighted light vehicle noise reduction at low speeds. Measured insertion losses range from 1.1 dBA to 3.6 dBA. The higher noise reductions are found to be associated with an increased ground effect.

Van Renterghem, T., Attenborough, K., Maennel, M. et al. (9 more authors) (2014) Measured light vehicle noise reduction by hedges. Applied Acoustics, 78. 19 - 27. ISSN 0003-682X

There was minimal noise attenuation that could be attributed to the coniferous trees at the 15 study sites examined. Attenuation was not correlated with tree stand age, height, species, or density for these sites.

Highway Noise Reduction Experiment. Virginia Department of Transportation. December 2008

It showed that Pithecolelobium dulce have the highest noise reduction of 10.12% [9.9 dB] at 20 m distance,

U.R.Pudjowati et al. "Estimation of Noise Reduction by Different Vegetation Type as a Noise Barrier : A Survey in Highway along Waru – Sidoarjo in East Java, Indonesia"
Noise is a kind of kinetic energy, and energy is conserved. The only ways to decrease the noise that reaches your home are reflection and absorption. (Increasing the distance to the road is not feasible.)
Reflection alternative
This means a tall solid wall.
Here is a white paper that describes the principles of sound walls. In order to be effective, a sound wall must have no holes and be tall enough to prevent diffusion around the top.
Absorption alternative
This means converting the noise energy into heat energy (imperceptible in landscaping situations). Materials that absorb noise energy well tend to have complex internal structures. Examples include mulch, rough lumber, and perforated sound absorbing panels.
Psychological alternatives
Noise perception can be subjective. Noise can be added to mask the road noise:

Flowing water features.
Tipping bamboo fountain (Shishi-odoshi).
Wind chimes.
Habitat that attracts chirping birds.
Comment: The hedge would be very effective at helping to hide what could turn out to be an ugly sound wall. (I'm thinking the concrete monstrosities along freeways - a wood fence would be much nicer looking.)
Comment: +1 for providing references and not just opinion. Maybe also mention that "A" weighted means that measurements reflect the ear's different perception of high and low frequencies, so these dismissals are not just an air pressure / vibration measurement but take into account what noises we are sensitive to, making the conclusions even more relevant.
Answer: Adding hedges will not do much to muffle the sound. You would need a totally dense hedge like you see in a garden maze which would be impractical.
You would be better off upgrading your windows to double pane gas filled ones.
Answer: Not really.
I live along a highway, and even a substantial row of mature trees and undergrowth doesn't do much. You need density and you need full obstruction. A hedge provides neither.
Do like I do and look forward to the electric vehicle revolution. Hopefully tire manufacturers have discovered that they'll be the biggest noise culprits and are working to reduce sound output in new models. Also file complaints with the city over juvenile drivers with illegal exhausts.
Comment: I really hope the tyre manufacturers don't do very well, because on a bike or on foot it can be important to hear cars coming up behind, and tyre noise is better than nothing in the absence of engine noise.  They are trying to improve efficiency,and that might make them quieter anyway
Comment: most cyclists and pedestrians who get hit aren't at fault, but may be able to take evasive action. Cyclists in particular are often clipped from the side while being overtaken and knowing that a close pass is coming has saved me more than once. We need multiple layers of protection. Do all Nissan Leafs (as an example of a particularly quiet EV) have radar? I know not all Priuses do but they're only electric at low speed
Comment: It's a poor strategy to rely on noise in most environments, as we have so polluted our airwaves that you're as likely to not hear it anyway. The disproven fallacy of loud pipes saving lives is a testament to that. Instead, positional radar will continue to evolve until cars see us nearly 100% of the time and avoid incidents nearly 100% of the time. That's a far better rate than we achieve as humans.
Comment: in all but the noisiest environments (i.e. even on many urban roads) I can not only hear a car coming up behind and how far but get a good idea of where they are laterally too. ICEs give me cues from engine note, but I can easily hear a tesla coming up behind. It will be a very long time before the majority of cars sold have any radar, never mind the majority of cars driven; even with almost perfect sensing, better than humans, you've still removed some of the vulnerable road users' ability to take defensive action. Then you get to blind people
Comment: I can hear well, too, but that's not the issue. The issue is _attention_. It takes a significant sound to draw attention from someone who's mentally elsewhere, and they're the ones getting hit. Also, we don't need a majority of cars to have radar--we need the ones with quiet propulsion and quiet tires to have radar. That's coming along nicely.
Answer: From the photo, it looks like there's not a lot of distance between the road and your house, and worse, you're well above road height.
If there were more space,and local codes allowed it, the best barrier is a berm.  Even a 4-or 5- foot high berm will deflect a lot of the sound upwards and away from your house.  Add a solid fence on top of that and it'll get even quieter.
Answer: Where a hedge can be useful is screening a fence or wall from view.  The wall or fence is then what does most of the noise-blocking.
A dense hedge on the outside of a wall will also, to some extent, reduce the effect of sound reflecting off a masonry wall at your neighbours across the street.  To a lesser extent they also help by extending the height of the barrier if the maximum fence height is limited.  Hedges also take time to grow to full height/density.  Even if you buy fairly tall specimens to start with they need to fill out.
Any structure needs to be solid and heavy; while ordinary close-boarded fencing will help, there are specialist noise fences (UK supplier, but I've seen hits from other countries) which use thicker timbers designed to overlap very well.  They're not cheap, and need to be installed properly.
As noise fencing is more specialised than improved windows, the windows might be the first thing to look at.  Any draughty gaps or deliberate ventilation let in noise, but if you only have a single layer of glass that's the easiest thing to address.  In some places, traditional wooden shutters over the outside of the windows (or more modern UPVC-clad shutters operated from indoors) are used to reduce noise.  I've seen these in hotels near airports/main roads in Germany, for example.

Could hedges help in reducing noise?


Help with some book titles

Question: 重生之妙手医心

I don't get this because of "妙手医心."  What does it mean?  A wonderful hand and a doctor's heart?

大哥这种生物,少惹为

What is "少惹为?"

魔天记

Is it "devil's diary?"
Answer: 妙手: magic hands is a metaphor for skilled person (painter, writer, doctor, etc). There is a phrase '妙手仁心' magic hands and kind heart which is used to praise good doctors. '妙手医心' means the same.
少惹为: you're missing a character, it should be 少惹为好 er 少惹为妙, meaning the less provocation the better. The whole sentence means better not provoke the boss.
魔天记: 魔 generally means devil, 天 means sky or heaven, 记 means diary or story. Without reading the book (suppose it is a book), the exact meaning of 魔天记 isn't clear even in Chinese.
Comment: 魔天记 = story of magic days
Comment: 魔天记 could mean "Tales of Magic Heaven" or even "Tales of Devils' Heaven".
Answer: Answer from @NS.X is good enough. But I think you may need a little more background :)
These books are all online-novel, in China it's kind of industry, writers need to type 3000-5000 or more characters per day-so you can imagine the quality...
And their title, sometimes it's just simply add cool characters together(天,地,神,魔,龙,etc) or replace some characters from proverb. They dont have actual meaning in classic Chinese. So if you are trying to translate, better use their concept rather than literally meaning.
Hope this may help.

Help with some book titles


roof or drylining walls first

Question: We are renovating our house, re-roofing, dry lining and getting windows replaced.  The builder recons he will do the dry lining first and then the roof . Does it matter in what order this happens
Comment: By dry lining, you mean adding drywall?
Answer: Well, does your roof leak now? If it leaks and they put in new drywall, and it rains, the new drywall could get leaked on & possibly ruined.
Even if the roof doesn't leak now, they have to tear off the old roof to put a new one on, and they really should wait for good dry weather to do that but sometimes they don't, or unexpected storms appear. So without a roof you almost certainly will have leaks inside the house, again possibly ruining new drywall.
So, with good weather it shouldn't matter. But if it rains & leaks, it will matter. Why not do the roof first?

roof or drylining walls first


How to do a FULL system backup

Question: I have been looking around but I cannot seem to find anything that will do a full system backup. Programs like deja dup let you pick which folders to backup but I want the entire Ubuntu OS and everything on it backed up onto an external hard drive. There are probably ways to do it in the terminal but I don't like to do those kind of things in the terminal and would rather have a GUI for this. Does anyone know of an application that can do FULL system backups and if so how?
Comment: Just keep in mind "full backup" is not necessary and the resulting backups are large. You only need to back up user files (/home and /root) as well as any system files you edit. Personally when editing system files, I advise you make a backup (I save the original file as file.org), leave a comment as to you configuration (comments usually start with a # or a ;), and keep a copy of the file(s) in /root (such /root/etc/file). The only other exception would be servers, and in that case you would back up the server data (config files and /var/www for example).
Comment: You can also generate a list of all installed packages. See http://askubuntu.com/questions/9135/best-way-to-backup-all-settings-list-of-installed-packages-tweaks-etc
Comment: So what you are saying is if I just backup /home and /root I can get Ubuntu back to the way it is now even if something happens and Ubuntu gets messed up?
Comment: See the link I just gave you. I use to do a "full back up" in the way you are asking, but the resulting backup files are large and more difficult to restore, IMO.
Comment: Does root infer home if residing on the same partition?
Answer: You can use Deja-dup for this. If you want to just backup all of your files, then you just have to set Deja-dup to backup your entire system. Make sure the Deja-dup does not backup your backup location or it will run into problems. If you are backing up to an external hard drive it will probably be mounted under <code>/media/$USER</code>.
I would recommend creating a system image because it saves all of your partitions and can be used to do a full system restore. It is common practice to do small backups of your home directory every day and then every week create a new system image. This way if your system gets breached, you can just restore a previous system configuration without worrying about your system getting screwed up.
Comment: Would you happen to know what setting in Deja-dup will do a full backup because as I am looking at it I cannot find a way to do a full backup with Deja-dup.
Comment: You have to go to backup folders and select the root directory. Make sure that you exclude your backup directory! If you need pictures let me know.
Comment: @John Is the file created by using "DD" to create a system image a true system image and not a "diff" backup?  In other words, could I use it to restore my system on to a "blank" hard drive?
Comment: @RobertOschler When you use DD you are creating a raw representation of the disk as a file. So yes, all you would do is create the image file using dd, then write the image file to a device using dd. The drawback of this is that there is no compression so you need a hard drive that is at least the size of the source hard drive to do the backup.
Answer: Use clonezilla on live CD/USB, its free and powerful. With this you'll be able to fully backup/restore disks/partitions including OS, userdata, etc..
Check : http://clonezilla.org/
Follow this to use : http://clonezilla.org/clonezilla-live.php#use
Comment: Clonezilla is the best, but every time you want to do a system image you have to boot off of the live CD. It's worth it to have the extra backups though =)

How to do a FULL system backup


Minimum Sink Rate in Sailplane

Question: How do gliders ascend (either with an engine or thermal) at best rate of climb if it is very close to stall? Or they move up by sacrificing that best Rate of Climb. In image the best CL^3/CD is Minimum power required.
Comment: Glider (sailpane) pilots frequently thermal at "close" to the stall speed.  Given the slow speed and high angle of bank, spins are a real risk if the aircraft is capable of spinning.  This is one reason spin recovery - in the UK at least - is part of a glier pilot's annual check.
Comment: Can you clarify what the question is?
Answer: Usually, the designers make sure that the margin between the minimum sink speed and stall speed is larger. Take a look at a real example: the flight polar of the ASK21, one of the most common glider trainers.

The lowest sink speed when the glider is fully loaded (G/S is the wing loading) is marked with "ger. Sinken", and at 82km/h it is about 15km/h (+22%) larger than the stall speed (~67km/h). In gusty weather the pilots will fly at higher speeds, trading off performance against safety.
On a more general note, assuming constant zero-lift drag and parabolic induced drag, the mathematical equation to calculate the factor between the stall speed $V_S$ and the minimum sink speed $V_{\textrm{min sink}}$ would be the following one:
$\frac{V_{\textrm{min sink}}}{V_S} = \sqrt{\frac{C_{L,max}\cdot k}{C_{D0}}} = \sqrt{\frac{C_{L,max}}{3\pi \cdot C_{D0} \cdot AR \cdot \epsilon}}$
$C_{L,max}$ is the maximum lift coefficient attainable by your airplane,
$C_{D0}$ the zero lift drag, and
k the factor used for the quadratic term in the drag coefficient equation ($C_D = C_{D0} + k\cdot C_L^2$, which depends mainly on the aspect ratio AR of the wing and the oswald factor $\epsilon$)
Comment: This is not really intentionally - the increase in sink rate close to stall is the result of growing flow separation. Without that, sink speed would decrease right up until stall.
Answer:
How do gliders ascend at best rate of climb?

They do it by closely watching speed and stick forces.
You are right, when aspect ratio is high, the polar point of minimum sink is at a very high lift coefficient. If we use the parabolic drag equation, minimum sink c$_\text{L}$ over aspect ratio looks like this:
$$c_L = \sqrt{3\cdot c_{D0}\cdot\pi\cdot AR \cdot\epsilon}$$
With a minimum zero-lift drag coefficient of 0.008 and Oswald factor $\epsilon$ = 0.98 we get
<code> Aspect  | minimum sink rate at
 ratio   | lift coefficient:
--------------------------------
   15    |   1.053
   20    |   1.216
   25    |   1.359
   30    |   1.489
</code>
With a standard-class glider the last polar point is probably not flyable at all. Flaps not only help to shift the laminar bucket up and down, but also allow high-performance designs to actually fly at their optimum polar points.
When thermalling I pay close attention to stick forces and have tried out stalling the glider before. Every type behaves differently, so I recommend to gain some altitude when flying a new type and then stalling it several times, with a variety of bank angles. In most cases control forces in roll become really low and some even will show stick forces into the circle right at stall. Depending on the airfoil on the outer wing, in that case you quickly pitch down a bit or throw the stick to the other side to support the stalling wing.
In sailing when you are close to the wind you should always play a bit with the rudder and watch the leech of the sail. If it starts to flutter, let go a bit on the rudder and then slowly tighten it again.
The same should be done when thermalling. When you know your plane, this will soon become second nature. Especially the most modern gliders can happily be flown down to very low speeds, but then their sink rate goes up because a lot of the wing has already separated airflow. Here it is better to fly at a faster speed: Controls are stiffer, control response is better and you circle at the same speed as everyone else in that thermal.
With weak and blue thermals (no clouds) you need to fly very tight circles because then thermals are narrow and climbing is only possible at steep bank and low speed. But this is hard work - most pilots fly for fun and happily accept a slightly lower climb rate but can fly at a lower bank angle and without paying close attention to speed at every moment.
Comment: It's worth clarifying that 'what would give the minimum sink rate in static air' is not the only, and not the most important factor that pilots take into account.  Typically the pilot will try to spend a high proportion of their time in the areas of strongest lift.  While the AoA might affect the glider's performance by a few tens of feet per minute, staying in a strong thermal core can gain several hundred fpm in a climb.
Comment: @Frog Yes - and where is the updraft strongest? At its center, which can be rather narrow. Which in turn requires tight circles. At high lift coefficients. If it weren't, gliders would mostly fly straight.
Answer:
either with an engine or thermal?

Well, with an engine the best rate of climb is Vy.  Lower angle of climb than Vx but faster.  This results in a higher rate of climb.
With a thermal we use V min sinken because the rate of ascent is thermal updraft speed - sinken rate.
At V min sink the aircraft has a steeper angle of descent towards earth but a slower airspeed, resulting in a slower rate of descent.
This enables the updraft to increase altitude as much as possible, with the added benefit of slower airspeed allowing tighter turn radii to stay in the thermal.
Notice soaring birds, such as eagles, have broad, heavily cambered wings, with slatted tips, to fly as slowly as possible in thermals.

Minimum Sink Rate in Sailplane


is there any problem if i reset my unrooted andoif mobile that is previously rooted?

Question: My phones play store is not connecting to internet it shows connection error.... and some of the app is not connecting to internet. I think factory reset may solve this problem but I have rooted my phone and then unrooted. what will happened if I reset my phone?   device name : Intex Aqua Q5 (released recently) currently no firmwares available on the internet.  Android Version : 4.4 kitkat
Comment: *"what will [happen] if I reset my phone?"* -- take backup first. You would lose third-party apps, apps data, all custom settings and more. I don't know how your stock recovery would reset the phone so take backup of internal SD card as well.
Comment: This seems to be an [XY problem](http://meta.stackoverflow.com/q/66377/192154). Instead of trying to get your supposed solution working: Why not rather asking the real question? Have you checked with the first-aid given in our [google-play-store tag-wiki](http://android.stackexchange.com/tags/google-play-store/info)?
Answer: Resetting your phone won't cause any problems, but all third party apps will uninstalled. If you don't want to reset you could try booting into safe mode instead.


Cell Shading Visible Only When Printed? Microsoft Word 2010

Question: I have a bunch of Word documents with tables in them. I was using Windows XP and Office 2007 when I created them. Within the documents, I often use cell shading (the little tilted bucket) to shade certain cells for them to stand out. I upgraded to Office 2010 and all of the documents continued to be fine.
We recently upgraded to Windows 7 which had Office 2010 in it. I'm reading everywhere that no version of Windows 7 comes with Office but this is at my job and whatever image they're using to upgrade all the computers to Windows 7 already has Office 2010 on it so I don't know.
Anyway, since the upgrade, the original cell shading of my documents isn't visible to me anymore. At first, I thought it had completely disappeared because it looks as if nothing is there but when I print the documents, they print with the shading as if nothing is wrong.
If I apply new cell shading, I can see THAT on the screen, but the original shading is "hidden" or something. Anyone know what might be happening?
Comment: This question really doesn't belong on a programming site, you should find some Office support.
Answer: Thanks! I find out that it has something to do with the way Office was programmed with installation that caused the colors to shift. Lowering the contrast of the monitor and the brightness restored the appearance of the cell shading, which in the current installation was thrown shades off from the original to the point of being invisible.


What does the US produce?

Question: I have heard several times that the USA has the largest GDP in the world and also the largest economy. But I hardly can remember a single thing made in the US that I ever used.
My auto is made in Germany. My computer has parts made in China, Thailand, Taiwan, by Korean and Japanese companies. My TV is made by a Korean company, assembled in Russia. The other TV is Korean too. My vacuum cleaner is made in Germany. My washing machine is made in Italy, the kettle is made in Czech Republic by a German company. My microwve oven is produced in China by a Korean company, my drill is of German origin, my refrigirator and gas oven produced in Russia. My cell phone is made in China. My razor is made in Germany.
I also never wore any clothing made in the USA. My clothing is mostly made in China or Turkey.
I also never ate anything produced in the USA, my food is mostly made in Russia, Ukraine and EU.
I can only name the following things that I used which were produced in the USA:

Computer programs (Windows)
Hollywood films
Airplanes (Boeing)

May be it is only my own (wrong) impression? But here is trade diagram for the US-Chinese relations:

I am pretty sure that for Russia the picture would be the same, with a difference that we mostly export raw materials rather than industrial production.
It seems it turns out that the US consumes a lot of goods, but exports only green paper. That said I wonder why it is considered to be the first economy in the world.
Answer: Much of what USA produces isn't for export (too expensive to compete with Chinese manufacturing).
For example, US manufacturing sector is 4Trillion (2002 data) out of 16T GDP, and in 2014 they exported 138 Billion/month only - less than 35% of what was produced! (see details below).
Also, some of what is produced (and exported) is intangibles: finance, health care, information, scientific/technical services, administrative services, educational services, management, entertainment. That is actually growing and hard to estimate because I never saw IP broken out.
(Total US exports were $2.18T in 2014)

Rough summaries can be seen below in the first chart. (Wikipedia)
As far as tangible manufacturing for export: this is covered here in great detail.
Especially download "Foreign Trade" FT900 report from Census Bureau, it has "Exibit 7: Exports of Goods by End-Use Category and Commodity".
Some rough data on exports (Monthly data Aug 2014):
<code>Total, Census Basis                 138 (all #s are in Billions)

Capital goods, except automotive    47B
      Civilian aircraft                 5B
      Industrial machines, other        4.6B
      Telecommunications equipment      3.7B
      Semiconductors                    3.6B
      Electric apparatus                3.5B
      Medicinal equipment               3B
      Computer accessories              2.8B
      Measuring/test/control instruments 2B
      Parts-civilian aircraft           2B

Industrial supplies and materials   44B
      (largest: Fuel Oil 6B; Other petro products 5B)

Consumer goods                      17B (no breakdown)

Automotive vehicles+parts+engines   13.5B

Foods, feeds, and beverages         10B
      (Corn is largest at 1B, then fish, wheat, juices/fruits)

Pharmaceutical preparations         4.5B (Viagra, baby!)

Cell phones/other household goods   2B
</code>
Comment: What is the difference between the top and the bottom charts? What is a sector of economy "wholesale trade"? Is it taking Chinese goods and selling inside the US for 5 times greater price? Is this the largest source of the US GDP?
Comment: If the most of what the USA produces is for internal consumption and given that the US is the largest economy, they should have exceptionally high standard of living, but this is not the case as the statistics indicates.
Comment: @Anixx - bottom chart is kind of irrelevant by scale but I think it's things not produced by private companies. Persons or government, likely.  I was just too lazy to edit that out of the image.
Comment: @Anixx - See the exports part of the answer for what they export.
Comment: I apologize that I don't have good #s for ~2013 USA sector manufacturing. I assume they didn't shift much from 2002
Comment: You name entertainment, education etc, but from your chart it looks like entertainment, education, company management services etc have totally negligible share - combined, smaller than disposal of waste! It seems the largest sectors are wholesale and retail trade. And they sell... well, mostly imported goods.
Comment: @Anixx - Yes, for total GDP they are small-ish. They are ~2T combined when excluding healthcare, compared to 4T for manufacturing
Comment: No person with whom I talked who were in the US said they had exceptional recreation or entertainment compared to other countries.
Comment: @Anixx - One of the most influential movie critics in Russia ("Bad Comedian") greatly disagrees with you. As far as recreation - they just need to know which areas of which cities to visit :)
Comment: I think our largest export, currently, is refined petroleum products.
Answer: I am not sure that I will be able to answer your question to your satisfaction but I will at least try to discuss a number of misconceptions that need to be dispelled to gain any understanding of the modern economy.
Tangible consumer products are only a small part of the economy. The US (or, for that matter, Germany) also produces a lot of things you will never see in your home or backyard. Machines, military equipment, legal or financial services or even cattle fodder (one thing the US not only produces but also exports).
Incidentally, you wrote somewhere that military spending is "only" 5% of the GDP. It sounds like a lot to me and at the end of the day, US production is going to be the sum of all these "small" sectors. Unlike some other countries, it's certainly true that the US is not dominated by one or two narrowly defined sectors so there is no "one thing" the US produces above all else.
Brand and production are largely disconnected and added-value can be distributed in many ways. Your very first example is your car, which you claim is made in Germany. But the truth is that car makers just about anywhere assemble parts produced in various places, either directly by themselves or by other companies (maybe not in China and India but certainly in mature economies, including Germany).
Supply chains in this industry tend to be particularly complex but it's almost certainly untrue that your car is entirely made in Germany. Meanwhile, French factory workers go on strike against French car companies moving more and more activities to other places in Europe like Romania and Toyota advertises the Yaris as a car "made in France". It's just way more complicated than the name on the product might suggest.
More cogently, all major German car makers actually have plants in the US, producing for the US market. Much of the value is arguably provided by R&D workers and most of the profits are presumably captured by management and shareholders back in Germany but in terms of production, it's also happening in the US. So "German" cars is one thing the US produces.
Exports are another question entirely. I first thought you were located in the US and then realized you were not, which means most US-based services are not available to you and any US products you might own would have been imported. Now, why would you expect that the US necessarily exports something you might want and/or can afford? In principle, it is entirely possible for the country to produce a lot of things and be richer than any other country on earth without exporting anything at all.
As another, completely different example, let's consider the Soviet Union and its satellite states. They exported virtually no recognizable consumer products to the West and had a lot of difficulties being competitive or getting what they needed from the global market but they still produced something. In spite of all its problems, the SU industrialized Russia and became much more productive than traditional non-industrialized societies. Given its (relatively) large population, it did in fact produce quite a lot and manage to hold an arms race with the US for a few decades (before ultimately collapsing, obviously).
Now, in reality, the most successful economies are embedded in international trade and export and import many things but they also mostly produce for themselves. How this works out is a complex question in itself but there is no need for the US to produce your car for it to be rich and produce many things.
Finally, the balance of trade is yet another thing and it's closely connected to currency exchange rates. The US does export many things (not necessarily to China) but that does not mean it will have a trade surplus. In fact, the US has a large trade deficit but that's not because it does not export anything, let alone because it does not produce anything, that's mostly because China holds large amounts of dollars and keeps its products cheap that way.
Germany is a mirror example. Its economy has many problems, it has not seen any impressive growth or productivity gains of late but it's still quite successful at exporting some high-end tech products and because its main trading partners are locked in the euro, it can easily maintain a large trade surplus. None of this is directly connected to the size of the economy as a whole or the wealth of the country.
And as a matter of fact, as @DVK remarked in a comment, the US does still produce many cars, only for itself. So products for local consumption (including food!) would be another part of what the US produces, and quite efficiently so.
Services are a major part of mature economies. In the US and a bunch of rich European countries, somewhere between 70 and 80% of GDP. In Germany, it's 71%. Why that is and what that means is also a complex matter but you cannot completely ignore services (like you did in your question) and say anything meaningful about the US economy.
These services come in several guises. Some of them (legal or financial services, business consulting, etc.) are actually high-value services that the US exports. You dismissed Hollywood and software but those are not negligible either. Even if you are not personally seeing any of it, all this is part of what the country produces.
Other services might seem completely unremarkable to you. It's a well-known and quite interesting fact that even low-productivity sectors see an increase in wages as the economy as a whole gains in productivity. So hairdressers and sale clerks in the US might not be doing anything special but they sell their services for a higher price and they have a lot of purchasing power compared to people elsewhere in the world, just because they do what they do in a rich country.
You remarked somewhere that it seems that many US people are simply selling and reselling goods produced elsewhere and to an extent, it's completely true not only of the US but also of all other advanced economies (but they are also cleaning, cooking meals and selling houses). Furthermore, because these sectors are labor-intensive and have a low productivity, they represent an even bigger share of the workforce.
As a though experiment, imagine that soon robots will completely replace factory workers (something many people have been announcing for some time). Obviously distribution and ownership could be a problem but, as far as the economy as a whole is concerned, we would all be extremely rich without anybody doing any of the production. We could all pay each other to do seemingly simple services (which would become more valuable than manufactured goods which would then be plentiful) or maybe not do anything at all and still have a lot of the things produced by the robots.
In fact, it's an expected result of productivity gains in other sectors and it's a good thing. A lasting split between a competitive export-oriented sector and lack of growth elsewhere is a major problem in some countries (it was a concern in Ireland for example or in countries exporting valuable raw materials). A minority might be able to enjoy imported products and cheap services from the rest of the population but most will remain poor and the country is hugely dependent on the vagaries of international markets.
You might never set foot in a US fast-food and think that massages in Thailand are better but it's still a fact that none of the richest, most productive economies in the world are export powerhouses centered on manufactured goods or heavy industry (although one of the biggest, China, is, see below for more). Incidentally, full-time domestic servants, the most exclusive type of service you can imagine is common in poorly performing, highly unequal countries but virtually inexistent in mature economies.
All this might sound counterintuitive and anticlimactic but it's a fact that low-productivity services that have to be sourced locally are a large part of what the US currently produces. And because other sectors (from agriculture up) are extremely productive, those services are valued higher and everybody can be richer than in an economy without such productivity.
There are a few other things that makes the US seem richer but might not reflect any actual structural difference. For example, US workers tend to work more (over their lifetime) than, e.g., Europeans. Because of that they do produce more "stuff" (to quote a recent advertisement) that shows up in the GDP calculation but they have less time available for other endeavors.
By contrast, what makes both Europe and the US much richer than they were a few centuries ago is increased productivity. 300 years ago a shoemaker could make perhaps a few pairs of shoes a day. Now a handful of workers with the right machines can make thousands of pairs of shoes. We can choose to use this increased productivity to have more shoes or to have more free time while still having the same number of shoes but we are much richer in any case.
Another thing is that domestic production is difficult to account for in the GDP. If you cut your family's hair, there is no monetary transaction involved. If a state hairdresser cuts hair for free, you can't easily put a price on that either (OK, I don't know if there ever was something like that). Statisticians do have a few tricks to take those things into account but it's not a perfect science.
To the extent that the US went further than Europe in moving some things outside the realm of domestic production and to the private sector (eating out at McDonald's compared to cooking at home to use a cliché), it could have a seemingly higher GDP while producing essentially the same thing (e.g. a meal).
US healthcare, in particular, is a bit like that. It's good but it is extremely expensive compared to healthcare in similar countries with no obvious benefits in terms of outcomes (you can cherry pick a few statistics to make it look better but there are really no large differences, e.g. in life expectancy). And it does appear in national statistics at the level it is paid for so that is a not-insignificant part of what the US "produces".
Finally, don't forget that the US is big (and China is even bigger). You mentioned GDP (not GDP per capita, purchasing power parity, productivity or whatever but just GDP). One factor behind it is obviously population size. There are a few countries that might be richer than the US on a per capita basis and quite a few that are only slightly poorer but all those that come close are smaller in terms of population. In total, the US also produces a lot because it is simply bigger (the EU is keen on lumping all its member states together to produce impressive stats but those are still independent countries).
But China has or is going to take over no matter what. You might debate the details of its statistics or the exchange rate, it might face a serious crisis at some point in the future and it's still much poorer than the US, Japan or Western Europe on a per capita basis in any case but it is mind-bogglingly huge. And so it already has a very large GDP. That's all it takes to be the world's first economy.
Comment: Great answer overall!  To your comment that healthcare in the US is more expensive without obvious benefits, I would like to mention that the US leads the world in medical research and pharmaceuticals... work that is done by the individual scientists "for the greater good" but which often has only a slight impact locally, and which is exported essentially for free through the medical journals.
Answer: While I'm not going to argue with what others here have written, I can't really give anyone a passing grade since I don't see any references to military production anywhere. Any discussions of this sort that don't include the military are dropping the ball.
What the U.S. produces and spends on the military dwarfs just about everything else. Note, that you could probably say that for many countries internally (i.e. within their own economies). The U.S. however, is a juggernaut when it comes to this type of spending.
On this Wikipedia page, you can see the top ten producers (but not all countries are represented). Of those, seven are U.S. companies and just those seven companies produce about $140B annually. The U.S. defense budget was about $640B last year (equal to the next nine countries combined). Not sure what they imported as these numbers don't look very solid but here it suggests <2%. While I'm sure that military labour and other costs are significant, e.g. maintaining bases, ships, etc…, I think it's safe to say that a lot is spent on production as well. I'll give just one example, the Gerald R. Ford carrier, which cost an estimated $12.8B and is still perhaps a couple of years from duty. I believe that there were plans to run ten such ships in the coming years. Consider as well that an aircraft carrier doesn't go to sea on its own. It will be joined by missile cruisers, destroyers, supply ships, subs, and the proverbial kitchen sink (and don't forget all the aircraft that the carrier hauls around).
Comment: Possibly, but officially military spending is just 5% of GDP.
Comment: Military spending is big in comparison to the federal budget of ~4T, it's almost irrelevant to the GDP that is over 16T
Comment: Only? Industry makes up 19% of U.S. GDP. What does the U.S. produce that exceeds this? Your question was about why you didn't own anything made in the U.S.A. Well, a huge chunk of what is made there isn't available in your local Best Buy.
Comment: On a separate note to someone else's point… If you own an iPhone/iPad, it may be assembled in China but much of its financial value flows to other nations' economies (e.g. Korea, Taiwan, and of the course, the U.S., etc…). And while the world is changing, a significant portion of the value in most computers went to Microsoft. And everyone who uses Google or Facebook, et al, is also adding to the GDP of the U.S. Finally, their largest trading partner is Canada. Lots of natural resources (e.g. lumber, oil, actors) flow south, get processed and return as finished goods.
Comment: I've already mentioned Windows, but fairly speaking Windows is now made in India. Regarding Canada... well, I never used anything made in Canada either except a U.S.Robotics dial-up modem in the 1990s, gifted to me at a birthday (and it was much more expensive than other options available but many believed those times that Canada's modems were the best, actually it worked quite below average).
Comment: It has been pointed that the US economy is services-based. But I never used any US services either (except the software as I mentioned). The charts above show that 2/3 of GDP is created by wholesale and retail networks! This means that the majority of the US GDP is re-selling Chinese(imported) goods for greater price, and nothing more!
Comment: @mockman - Most military spending is either salaries, or already included in the #s for industrial economy (see Boeing)

What does the US produce?


Euler's Totient function bound

Question: Do there exist any integers $n$ such that Euler's totient function $\phi(n) < n/5$?  How should I approach solving this problem?
Answer: We know that
$$\varphi(n) = n\prod_{p \mid n} \left( 1 - \frac{1}{p} \right),$$
so your question asks whether or not
$$ \prod_{p \mid n} \left( 1 - \frac{1}{p} \right) < \frac{1}{5}$$
can ever hold. In fact, the limit of the product of terms of the form $\left( 1 - \frac{1}{p} \right)$ is $0$ (which is equivalent to the fact that the sum of the reciprocals of the primes diverges).
So there are infinitely many numbers $n$ such that $\varphi(n) < n/5$, and in fact infinitely many numbers $n$ such that $\varphi(n) < n/k$ for any $k$. This also makes it easy to see that the smallest number $n$ such that $\varphi(n) < n/k$ will be the product of the first $\ell$ primes for some $\ell$.
Now that we know this, it's easy to check that $2 \cdot 3 \cdot 5 \cdot 7 \cdot 11 \cdot 13 = 30030$, and $\varphi(30030) < 30030/5$. $\diamondsuit$
Comment: @user2049004 This is a statement that comes from the totient function being multiplicative. To prove it, you must show that if $\gcd(m,n) = 1$, then $\varphi(mn) = \varphi(m)\varphi(n)$. There are many ways to do this (which are easily lookupable now that you know the word multiplicative), but it's commonly shown through the Chinese Remainder Theorem. (It can also be shown by hand more naively). Once you have that, you get this formula by evaluating $\varphi(p^k)$ and multiplying the correct prime powers to get $n$.
Comment: What is the name of that definition for the totient function?  I've never seen it before and my textbook doesn't seem to have it.

Euler's Totient function bound


Book where a brain/object controls humans so that everyone walks and moves in the same rhythm and pattern

Question: It's an old book about this thing controlling humans and making them do everything in the same set of patterns and actions, until someone tries to break free and destroy it.
Comment: Brain controls everyone to walk in the same rhythm? Must be http://xkcd.com/389/ "Keeping Time".
Comment: probable duplicate of https://scifi.stackexchange.com/questions/126937/unknown-science-fiction-space-book (which is newer but has an accepted answer)
Comment: @Otis the answers are the same (well, assuming they're correct), but the _questions_ are entirely different, so don't think it counts as a duplicate.
Comment: @JohnC, the general operating principle for scifi story ID questions is that "same answer" counts as "duplicate." This wouldn't be closeable until the OP confirmed via comment or acceptance, anyway. I just put the link in anyway to help make it easier for anyone coming to this page to find the other answer.
Answer: Possibly A Wrinkle in Time, by Madeleine L'Engle. The characters travel (via tesseract) through several dimensions, one of which is controlled by IT - a shadowy, disembodied brain that makes everyone behave identically. For instance, children bouncing balls on the sidewalk in rhythm. When one child makes a mistake, he's taken off and punished.
IT doesn't get destroyed in the book, though. Instead, the main character, Meg, rescues her brother, Charles Wallace, from IT's influence and they escape the planet.
Answer: "We" by Yevgeny Zamyatin has people walking, even eating in sync. It was written in Russian amd published in 1921. There's no over seeing brain or computer, but absolute conformity is driven by ideology instead. Could this be your book?


PDF size from PNGs very small

Question: I created a 25 page pdf with acrobat from 25 png files approx 65mb each.  They are 11x17 @ 300dpi so quite large.  When combining files I made sure to choose the large format for print but pdf size is only 15mb - only approx 100th the size of the 25 files.  On screen the pdf looks ok, but I'm just wondering how this is possible without having lost tons of data?  Are the pdf pages truly the same quality as the original png files?  If not, how can I create a pdf with full resolution images?
Answer: If your original png files are very highly compressible - mostly a single flat colour, for example - and you originally saved them without using compression, then Acrobat might choose to compress them without asking you. PNG compression is lossless, so it would probably not bother asking, just do it. then the final product would be smaller, yet would be pixel-for-pixel the same as your original.
Comment: yeah that makes sense but not so in this case.  these are fairly complex photographic images
Answer: Acrobat probably saved the images within the pdf as compressed jpegs.
I just took a jpg image from a camera, a landscape shot, which came out of the camera as an 8Mbyte jpeg. I opened that in photoshop and saved it out as an uncompressed png file, which was 48Mbytes. (Compressed png would have been 21Mbytes.) I opened that in Acrobat Pro to make a pdf, and saved the resulting document as a pdf. Acrobat asked me no questions, but the total resulting pdf was 1.2Mbytes, so it must have compressed the file a great deal. The picture still looked OK.
For Adobe CC Acrobat Pro on a Mac, I can choose Acrobat - Preferences - Convert to PDF - PNG - Edit Settings - color and it offers a variety of lossy and lossless conversions. The above example used JPEG (Quality : Medium).
Comment: thanks, i assumed that as well, and mine look ok, but i'd love some concrete data on what exactly is being done.  Really, it would be great to allow choice of compression, and if that's possible, I'd like to know how.

PDF size from PNGs very small


Qt/C++: Signal for when a QListWidgetItem is checked?

Question: In my form I have a QListWidget which contains checkable QListWidgetItems. I'm looking for a way to capture the event of a QListWidgetItem being checked/unchecked. I don't see any such signal existing for this but maybe I'm wrong. What I'm currently doing is using the QListWidget::itemClicked() signal and checking the checkState of the QListWidgetItem, but this isn't what I want because this event happens any time the item is clicked, not just went the checkmark is toggled. Can anyone give some assistance? Thanks!
Comment: I think I can get around this using the QListWidget::itemChanged() signal, which is triggered when I check/uncheck an item, but it would also be triggered if I edit the value of the item which, although I'm not doing now, is still an imperfect solution.
Comment: Another problem with `QListWidget::itemClicked()` is that it doesn't fire when you use keyboard, e.g use the Space key to change the checked state.
Answer: Apparently no such signal is provided, your best bet is to use QListWidget::itemChanged(QListWidgetItem* item) , and scan the resulting item->checkState(). This should be a slight improvement over using itemClicked
Comment: I was mistaken.  itemChanged() is indeed the right signal to intercept.  It _does_ fire when the checkstate changes.  Be sure not to confuse it with currentItemChanged(), which does not.
Comment: itemChanged doesn't always fire; e.g. if you highlight the item, and press the spacebar repeatedly.
Comment: @CodeLurker: That sounds like a bug.
Comment: It is a protected Signal. I will face an error when I use this error as explained [here](https://stackoverflow.com/q/48059796/1080355).
Answer: An extra option is to use your own QAbstractListModel with a QListView. At first this does add some extra code as you need to add your own management code . But you do get a lower level access. Basically because the QListView will ask your model what to do. It will also relay input back to your listmodel where you can hook into it.
Alternatively you could subclass QStandardItemModel and catch certain edits related to changing the checkbox.