Songwriting and improvisation HowTos

Question: Are there any actual rules of how to write music? I mean there're guides everywhere in the Internet like "so you have scale, shapes of scale, chord progression over scale - let's go, do whatever you want with it until it sounds good". But of course it's not sounds good. You can play random notes and it just not sound out of place, but that's all. There's nothing specific about how to chose next note in riff, which chord better suit to chord progression, how to chose between different chord types etc. Or I just don't know what exactly to look for. So the question is there any real rules or should I experiment with things until I find what suits to me because it's the only way? And if there is, what should I read about?
Answer: In the sense that music is art, there aren't rules. There are no music police who will put you in jail for parallel fifths.
But, to the extent that musical art is about style, there are rules and conventions within styles. For example, you avoid parallel fifths in chorale harmonization, but in heavy metal parallel fifths are de rigueur.

what should I read about?

You should read music scores or song lead sheets, or whatever notation is used for the styles of music that interest you. The music itself is the primary textbook.
You didn't mention a particular style, but you used terms like riff and chord progression so I have a general idea. For basic technical knowledge get a book about how to read staff notation and a book on music theory. That will give you a technical, musical vocabulary. If you can, try your local library first to peruse many books before investing in purchases. Music books are sometimes expensive.

...do whatever you want with it until it sounds good...play random notes...there's nothing specific about how to chose next note...

Really?!? That's someone's songwriting advice?!? It sounds like a recipe for lots and lots of wasted time!
Most musical styles are about patterns and not randomness. Those patterns are the "rules." Randomness as a songwriting process is either a specific process, like cut-ups, or randomly groping around, because you simply don't know the patterns. Don't justify the latter through appeals to the former.

So the question is there any real rules or should I experiment with things until I find what suits to me because it's the only way?

There are rules. Do with them what suits you. Follow them, break them, extend them, re-write them, make new ones, etc. etc. Random guess work is not the only way. In fact, I would say this instead: how did the great musicians, the innovators you admire learn? I'm sure you will find most of them studied (formally or informally), applied common patterns (rules), and then made incremental changes to what they learned.
Comment: while I found the random notes comment funny, I'd like to add a personal experience to that: when working with singers around a melody, having them try to randomize some elements of the melody (transitions, ends, etc) sometimes brings up some fresh idea. I guess this is not truly random because the changes end up at intervals that make sense, but the "let's try to play with it" concept is not always wrong.
Comment: Yes, but that is a bona-fide method. Those singers surely learned common patterns and use a "random" exercise to get outside of familiar patterns. That different that hit and miss guess work in a beginner.
Comment: yes, that's true; it's random within a set of options that make sense
Comment: Maybe my point is more about the person. The OP is a beginner. Your singers are experienced musicians. The experienced musician is partly trying to get out of trained patterns, part using their experience to _make tasteful selection from randomness_. The beginner is simply lost in the woods. Such beginners sometime post their "discoveries" on SE, things like borrowed chord, other chromatic harmonies, that are well known. Very rarely is it something actual new.
Answer: Play lots of existing songs. (You CAN read notation?)   Copy and steal.  Eventually, develop.
Answer: There are no hard and fast 'rules', unless you want to write a fugue; waltzes need to be 3/4, but as far as writing something is concerned, I can't see anyone picking up a 'rulebook' and going systematically through them, applying as many as possible!
Knowing scales, chord families, rhythms, and listening are all good things, particularly as a starter. Any 'rules' that exist came from 'that sounded rubbish - don't use it again', to 'that sounds good - use it again'. Most people's first efforts end up in the bin. So don't expect miracles - yet.
Answer: Music is not merely a sequence of disconnected tonal events placed in time (at random) is the a temporal painting (I've heard this quote attributed to other musicians, like Zappa), it is the cumulative sum of all the events that have occurred for the duration of the song.  As such, even if you had a set of rules, without the understanding what a song is the rules won't help you.
Having a mathematical background I like to use the analogy of derivatives.  Music is not so much about what has been played at t = 1, and t = 3, and etc., about the "change" in time from 1 to 3, etc.  It's the derivative that counts.  Another comparison might be a movie.  A movie tells a story and it is not a bunch of things that happen.  In fact the viewer cannot really appreciate the story until it is all over and they replay it in their mind to "see" the juxtaposition of this or that plot twist to how it was set up an hour ago.  Music works in a similar manner.  We set up cycles, and melodic themes, and through that build a background in the listener's ear.  Even the untrained listener will remember what they heard, maybe even be able to hum it.  So when you solo or improvise you want to draw on the themes that were presented to the audience, at least a little bit, before going down the rabbit hole of free exploration.  It takes time and training to understand this fully.  The best training is listening.  Listen to music you like and try to identify patterns.  The opening lick of Ornithology bears a striking resemblance to Einen Kleinen Nacht Musik by Mozart (perhaps more so after some lubrication), the group of notes is the same.
Yes, there are rules of a sort in music but they are not like rules in other disciplines.  I wrote about this in another stack exchange question.  Artists study light, shading, color, and perspective, all very geometric, mathematical, and physics based elements of art.  But the artist is not bound by any "rules" to use them in a specific way.  Look at Picaso, Pollak, etc.  The education is there, the expression is unbounded.  Music has similar structures in it that are to some extent based in the physics of sound and vibration and physiology of how our ear works (and our brain too).  And yes it is true that movements of chords like V7-->I or IV-->I create certain feelings that ii-->vi would not create, or that it makes sense to use the C major scale over a C maj chord but at the end of the day none of that is a rule in the sense that you are looking for.
There are no rules to creativity.  There are guidelines (which you have found and seem to frustrate you) and there are musical styles in which certain rhythms, grooves, changes, and melodies are favored.  It is culture more than anything that sets up rules.  I would recommend taking the time to learn some of these guidelines and try to identify them in action in music you listen too.
Classical Western Harmony theory is very much worth learning.  Starting perhaps with multi voice homophonic harmony, i.e. where all voices follow that same rhythmic expression in time but sing or play different notes.  This is heard in choirs and guitar chord melodies.  When it comes to composing you may want to familiarize yourself more with the genre of music in which you want to compose.  Composers are often called upon to write music in a variety of styles.  Learn what's common among the styles and what distinguishes them.  One hint in this regard might be that they all use the I, IV, V progression in some fashion or another but have different phrasing or inflection, or different tempo.  When it comes to improv, especially in Jazz, a particular school of thought has emerged that teaches one to match a mode to each chord in a progression.  This is grossly misunderstood by beginners as an indication that (1) only those notes can be played over those chords and (2) all those notes must somehow be played over those chords, neither of which makes sense.  In reality the process of playing through these scales while the chords drone in the background (like on a Jamey Abersold album) is to acclimate one's ear to the harmonic texture present within those scales and how they sound against the chord.  In fact one can do this with the chromatic scale too.  A better approach, advocated by Jerry Coker, is to keep a journal of licks and phases that you think sound cool.  He recommends thinking of 5 new licks a day for some extended period of time.  Then work on fitting these lick into tunes, perhaps right into the melody.  After a while you've rewritten the song, and that's a solo.  Improv is variation on a theme so it stands to reason that if you're soloing over someone else's tune the best place to get ideas is the song itself.
On the topic of fitting a scale or mode over each chord there is a classic example of a scale played over a chord where one has "out of tune notes" and it works great, the Blues.  The chords of the blues are not in one specific key, and the scale used is not one of the modes that would classically fit over any of them.  That's all the proof I need that the rules were meant to be broken.  What counts is setting up the musical story, like a movie, where the lick you are going to play in a minute is set up by the lick you're playing now.  To this end I don't mind telling you my favorite starting notes over a major 7th chord are the #5 and b9.  I'm not going to drone on those notes (maybe a little) but they will lead to a melodic idea that is dark and heavy, but eventually resolves.
Answer:
"But of course it doesn't sound good... You can play random notes in a
scale and they just sound compatible, not good." (I paraphrased a
little. :D )

Sounding "good" is somewhat relative. We can probably agree on songs that we'd both consider good or bad, but there will also likely be differences.
I think a lot of folks are internally driven by a compass, pointing in the direction of what's "good". I think it's an important thing to have and one should listen to it, but keep in mind it's also subject to influence and can change over time.
Learning your favorite songs or how things that sound "good" are played will help improve your relationship with that compass. However, exploring music, breaking things apart, gluing pieces back together in different ways and/or changing them altogether are also fruitful parts of that process. You might even be doing this already when you hear songs that are 'almost amazing/perfect' (or that you don't like), just making substitutions left and right in your mind for how a lyric or melody 'should' go.
The answer so far has been about musical expression and developing an inner voice because I think that's likely what's underlying the question. For the question itself though, I agree with others, "The code is more what you'd call guidelines than actual rules." Due to this, the writer often still makes musical decisions of what is "good" in these systems.
Also, there's not really a single "code", as the thought processes and motivations of the people that practiced their style of music during their time are often considered. For example, chapter 2 of Kennan's 'Counterpoint' is about how to write "good" melodic lines (for counterpoint). A modern take on creating and adding a melodic line might be something like Friedland's 'Building Walking Bass Lines'.

So the question is are there any real rules or should I experiment
with things until I find what suits me because it's the only way?

I would say there are guidelines to help your musical decision making that are accessible, but they are not really rules intended to make those decisions for you. It is very fruitful to learn pre-written things like scales/shapes/songs AND you'll want to try experimenting with those things and make your own musical expressions (improvise on top of songs, use scales to come up with melodies that sound and feel "good", learn different small licks and try to put them together (glue them by adding additional notes or chords or some musical expression if they don't fit together at first), etc...)

And if there is, what should I read about?

Before purchasing books and things, you might be interested in sections 6,7, and 9, of this music theory site which are for 'Triads', 'Roman Numerals and Cadences', and 'Harmonic Progression and Harmonic Function'. I imagine the takeaways are to get a sense of how chords are built, how they relate to scales, where the harmony of the 'Roman Numerals' comes from, and some examples of popular progressions. At a least, the site as a whole looks like it has some breadth and is skimmable, so maybe poke around and familiarize yourself with the notions/terminology there to help with future searches.

Songwriting and improvisation HowTos


How do I get the touch event on a body in JBox2d

Question: I have various bodies rotated at some angle with the help of Box2d in LibGDX. What I want is to destroy the body when I click on it, but the problem is that I am not able to get the area definition of the body so that I can check whether my touch point lies inside the body. I tried using actor and its hit() method but it's working only if I don't rotate it. As far as I know, once I rotate the body, its bounds are not rotated.  How can I check the Touch event in a Body?
Comment: Hi Jagdeep. I don't have any experiences with Box2D (I'm working with Slick2D right now) so I'm just gonna make a suggestion. In Slick2D, we have an object called the Shape, which defines the dimensions of a Sprite on the screen. For a rectangle, for example, we have four points, indicating the four vertices. In order to detect if the user clicked on one of the sprites, we check if the x an y points of the mouse click (or touch) are inside the points defined by the Shape. Maybe Box2D has a similar way to find out the objects' dimensions and position.
Comment: Hi Lucas, I cant use rectangles for the touch events because I am rotating the bodies to a certain angle and rotating of rectangles along the bodies is not possible as I know.
Answer: Create Box2d fixture for your touch (and attach it to body), set it to be a sensor, place it where your touch event occurred. From now on, you can check every body that collides with your sensor. And because you are using sensor, simulation will not respond to such collision(s), but will report them instead. Here's Box2d manual, look at chapter 6.3 about sensors.
Answer: You could assign a sprite  to your box2d body.
Form example I created a circle dynamic body with a radius of 1f, than I assigned to it a sprite (a red ball) that fits exactly the box2d body. Now it simply checks if the touch lies into sprite width and height.
Example Code:
   private void checkInput () {
                   Vector3 touchPos = new Vector3(Gdx.input.getX(), Gdx.input.getY(), 0);
                   camera.unproject(touchPos);
                             if (touchPos.x > sprite.getX() && touchPos.x < sprite.getX() + sprite.getWidth() && touchPos.y > sprite.getY() && touchPos < sprite.getY() + sprite.getHeight()) {
                body.setActive(false);
              world.destroyBody(body);
}
                      }

Answer: User touches the body only if he touches some of Fixture's contained into this body. This mean, you can check every Fixture of Body using testPoit() method:
public class Player {
    private Body _body;

    public boolean isPointOnPlayer(float x, float y){
        for(Fixture fixture : _body.getFixtureList())
            if(fixture.testPoint(x, y)) return true;
        return false;
    }
}

Next, you need to create InputAdapter like this:
public class PlayerControl extends InputAdapter {
    private final Camera _camera;
    private final Player _player;
    private final Vector3 _touchPosition;

    public PlayerControl(Camera camera, Player player) {
        _camera = camera;
        _player = player;
        // create buffer vector to make garbage collector happy
        _touchPosition = new Vector3();
    }

    @Override
    public boolean touchDown(int screenX, int screenY, int pointer, int button) {
        // don't forget to unproject screen coordinates to game world
        _camera.unproject(_touchPosition.set(screenX, screenY, 0F));
        if (_player.isPointOnPlayer(_touchPosition.x, _touchPosition.y)) {
            // touch on the player body. Do some stuff like player jumping
            _player.jump();
            return true;
        } else
            return super.touchDown(screenX, screenY, pointer, button);
    }
}

And the last one - setup this processor to listen user input:
public class MyGame extends ApplicationAdapter {

    @Override
    public void create () {
    // prepare player and game camera
    Gdx.input.setInputProcessor(new PlayerControl(cam, player));
}

Read more about touch handling here


Pantheon files sort by accessed

Question: Is it possible to sort files in Pantheon according to when they were last accessed? I used to be able to do it in Nautilus when I was running Ubuntu and even show the access time under the file's title. It's especially handy when keeping track of which series episodes I've watched.
Comment: I think the answer is no, but why is it flagged to close? Installing Nautilus for a purpose like this is a good idea. It has no conflicts in eOS.
Comment: I agree. Technically it wouldn't answer the question though would be a useful answer. Do you have reliable installation instructions for Nautilus you could post?
Answer: There are a number of outstanding wishlist bug reports requesting the ability to show and sort by columns other than those currently provided in List View.  Limited developer resources means this may be not addressed for a while.

Pantheon files sort by accessed


How to keep polling GitHub repository and get commits by it's messages on a regular interval using Jenkins?

Question: I need to know how to write a Jenkins job which polls a GitHub repository continuously and send an email of commits made to that repo.
Answer: Considering you have proper credentials in Jenkins and admin right for Git repo, Create a webhook between Jenkins and your Git repo. Webhook will help you push (reverse poll)the commits. You can use jenkins DSL (groovy) to operate on that Git repo by using Git commands. You can use specific Git commands to list Authors of last commits (or any other requirement) and Use email-ext (or any other) plugin in jenkins to be able to send email through DSL.
One line reference to list Author (yeah..it works as it is in any Git repo)-
git log -1 --pretty=format:'%an'
My reference of email to culprits if something goes wrong my jenkins build
step([$class: 'Mailer', notifyEveryUnstableBuild: true, recipients: emailextrecipients([[$class: 'CulpritsRecipientProvider'], [$class: 'RequesterRecipientProvider']])])


How likely will 2 normal bacteria "attack" each other if they infect the same parts of your body?

Question: I read this interesting article online about how deadly bacteria are known to attack other deadly strains of bacteria.
https://www.google.com.sg/amp/s/phys.org/news/2013-02-deadly-bacteria-remarkable-precision.amp
I am wondering how normal bacteria that infect us like those that cause strep  throat and so on also have the capabilities to attack other bacteria and how feasible it is to use this as a treatment for bacteria infections by introducing harmless strains od bacteria to fight pathogenic versions (maybe like probiotics?)
Answer: Mixed bacterial populations, where not engaged in some kind of mutual or commensalistic relationship, are constantly at each others throats over resources. Even then, sometimes it's just rate of growth isn't terribly bad for each commensal. Not just nutrients, for example, but also precious space to colonize or attach to. There's a good review here, and among some of the tactics direct killing by antimicrobial production is an option. You also have other factors, however, such as secretion of molecules that impair attachment or quorum sensing. Also, virulence factors that give a competitive edge such as evading immunosurveillance (encapsulated B. anthracis strains vs unencapsulated, for example).
So here's the hard part: you want to engineer an attenuated bacterium that goes in and attacks a pathogenic strain. While I'm sure possible, you would certainly need to ensure that what you take away to attenuate your strain doesn't gimp it in vivo. You also need to realize that your target pathogen is very capable of simply "changing" itself to avoid dying to the engineered strain. Once your mechanism of action has been defeated, your product has been defeated. I think that it's fundamentally different from commercial virus-based products like T-VEC, as well, due to the level of variability.
One of my thoughts is your strain needs to be able to compete with the pathogen in the first place to stand a chance, which may be difficult if you cut out too many virulence factors trying to make it "safe."


what do selected vertex colors mean?

Question:
When I selected a vertex by clicking left mouse button on it,and selected vertex looked white.
And then for some reason I selected the vertex by dragging left mouse button around it, then selected vertex looked orange.
I wonder why vertex colors are different in each case and  what each color means.
Answer: The white vertex is the active selection, and the orange vertex is not active.
Comment: thank you for answer
Comment: Sure! It's actually a feature, because you can use the active selection as your pivot point, your center for snapping, lots of stuff. For example, when you rig a model, select a bone, then another bone, and press shift-ctrl-C. Blender will create a constraint on the active bone targeted to the selected bone. You can also use this feature to parent selected object to active. Something I often do is copy/link data from active to selected.

what do selected vertex colors mean?


How to remove white spots of standing water on the marble tiles?

Question: I've tried a lot of time to clean marble tiles in my home but the tiles didn't get cleaned. How to remove white spots of standing water on the marble tiles?
Comment: Could you please explain what you tried so far?
Answer: Take some acid and some quantity of detergent mix it in one glass of water and throw it directly to white spots on marble after 15 minutes rub  the surface of tiles with any brush, all spots will vanish it's my personal experience but in this process you should have to avoid your skin from acid.
Comment: You shouldn't use acid on marble. Acids corrode marble and cause stains or even holes.
Answer: There are special, acid-free marble cleaners. Any household supply store should have it.
You can also use fine, stainless steel wool. Rub over the dry (!) stone with a dry stainless steel wool pad. The lime stains will be pulverized to a light dust that you can blow away or wash off with water. But be careful not to use non-stainless steel wool, as the abraded steel particles will rust and the rust will stain the marble.

If you have tried acid on marble, such as vinegar, citric acid, or other acidic cleaners, the stains you see may actually be the results of the acids destroying the polished marble surface. In that case, you need to polish it.
Answer: You can pour vinegar on that water spots leave it for few minutes and remove it with cotton.or you can also use lemon use to remove these spots.
you can also use some detergent, the process is you will take some water in the pot and add some detergent in the water, take small piece of cloth and dip in that water and then rub on the surface of tiles where spots are present.
Comment: Pouring vinegar on marble? Definitely not recommend!


Verb of sycophant

Question: Is there a verb form of sycophancy or obsequious, a word that would describe someone is conducting sycophancy. Google wasn't of much help.
Comment: One is or isn't a sycophant. It is a behavior. One does not conduct it.
Answer: One is or is not a sycophant. Merriam Webster defines this as: a servile, self-seeking flatterer.
If a person is one, they have engaging in sycophantic behavior for which there are a slew of verbs.
to curry favor, to boot lick, to fawn [over], to kow tow, to brown-nose, to grovel, to suck up to, etc.
Merriam Webster also explains it:
Did You Know?
In ancient Greece, sykophantēs meant "slanderer." It derives from two other Greek words, sykon (meaning "fig") and phainein (meaning "to show or reveal"). How did fig revealers become slanderers? One theory has to do with the taxes Greek farmers were required to pay on the figs they brought to market. Apparently, the farmers would sometimes try to avoid making the payments, but squealers—fig revealers—would fink on them, and they would be forced to pay. Another possible source is a sense of the word fig meaning "a gesture or sign of contempt" (as thrusting a thumb between two fingers). In any case, Latin retained the "slanderer" sense when it borrowed a version of sykophantēs, but by the time English speakers in the 16th century borrowed it as sycophant, the squealers had become flatterers.
explanation from Merriam Webster

Verb of sycophant


polo 2012 - driver door won't unlock with key but will lock

Question: I'm having an issue with my polo, the lock on the drivers door won't unlock but will lock once it's been unlocked via the passenger door using the same key. The key just spins infinately. It used to spin once or twice but eventually will unlock. Now it doesn't unlock at all.  I don't have an problems starting the car with the key either.  The switch inside the car on the drivers door works fine
Answer: Sounds like the barrel of the lock is damaged, maybe the striker for anticlockwise movement is missing or worn. [the actuator that pushes the locking mechanism back when you turn the key in the unlock direction]
Comment: Thanks for the answer even after so long. VW replaced the barrel for me since my car was still under warrenty. Perhaps I should be a little less heavy handed with my key.


Luggage storage options around Edinburgh Haymarket

Question: I need to stash my bag away in Edinburgh for a couple of hours on Sunday. I will stay close to Haymarket station so I am looking for an option in that area. There seems to be no storage facility in the station itself. I also found that there are storage options at Waverley and at the main bus station. Are there any options close(r) to Haymarket?
Answer: I recently stayed at the  Tune hotel Haymarket, directly opposite the Haymarket train station. (Also where the Tram-stop to the airport is)
They have a sign at the door, proclaiming that they will store luggage, also for non-guests, for a fee of a few pounds per day. (updated as per froderick's comment: GBP 5,- which I believe was per-item).
This service isn't listed on their website. that only lists the generic "luggage storage", which implies, in this case incorrectly, "guests-only".
Comment: Perfect! The cost is £5.
Comment: Glad it helped! and thanks for reporting back, I've included your price in the answer.
Answer: There are lockers at Edinburgh Bus Station near St Andrew Square.

luggage lockers - (can hold multiple bags) £5 small, £6.50 medium, £8
  large for each 12 hour period

Its not very close to Haymarket and if you were considering something more central then Waverley station luggage storage is also an option.
Answer: The conference centre has luggage storage, ask them whether you could use it. It's half a mile which is quite a bit with luggage, you can take the number two bus, two stops.
Comment: Presumably @chx means the number 2 bus - completely unnecessary to take though, EICC is an 8 minute walk from Haymarket.
Comment: Sorry, I was google mapping it half asleep :) fixed.


Kant on the Essential Ends of Reason

Question: In the CPR, Kant defines philosophy as "the science of the relation of all knowledge to the essential ends of human reason." What is meant here by 'essential ends'? This phrase recurs a few times but is never quite pinned down. Does it mean merely the goals of rational inquiry? If so, what are they? How does this differ from the ends of reason in the eyes of the rationalists, or the empiricists?
Comment: @JosephWeissman: Normally, the Critique of Practical Reason is abbreviated with CPrR because of this ambiguity.
Comment: Can you provide specific references inside CPR? I don't see this definition of philosophy in my CPR copy.
Comment: Try this:   https://books.google.co.uk/books?id=jVJ8CgAAQBAJ&pg=PT370&lpg=PT370&dq=philosophy+is+the+science+of+the+relation+of+all+knowledge+to+the+essential+ends+of+human+reason&source=bl&ots=FUtdBQoF9l&sig=unSxVzYZpYZq2X29t3WcujdZW04&hl=en&sa=X&redir_esc=y#v=onepage&q=philosophy%20is%20the%20science%20of%20the%20relation%20of%20all%20knowledge%20to%20the%20essential%20ends%20of%20human%20reason&f=false
Comment: "CPR" is ambiguous since Kant wrote both a critique of *pure* and of *practical* reason...
Comment: The quote is from the Critique of Pure Reason. But, I understand, Kant deploys the term 'reason' in widely varied senses at different points in his work.
Comment: Seems to me that the 'essential ends' may differ from philosopher to philosopher, so Kant does not have to define them. .
Answer: I can recommend a book, and this is a good one: Freedom and the End of Reason: on the moral foundation of Kant's Critical Philosophy, Richard L. Velkley.  (1989 U. Chic.).
P.S.  in fact your questions are so good either you have a born talent for philosophy (which is always possible) or this is a homework assignment, so I will leave it at the above suggested reading, which may satisfy the genius and student both.
Comment: Thanks! I'm no student of philosophy (yet), more of an autodidact trying to work through the broad strokes of Kant's general thought. My working understanding is that an end really is a sort of goal or outcome to be sought after, towards which reason works- what these ends are and where they come from vary based off the doctrine (empiricism, rationalism, transcendental idealism) in question.
Comment: Thank you. I hope you can lay your hands on the book I suggested. I was a bit surprised that it is still in print, but I'd still try to get it from a library or you may go broke buying books! Very good questions in my opinion.
Comment: Oh and let's see, if you are in Europe, Lucien Goldmann's book on Kant is a hidden gem, originally in German I think (Europa verlag 1945), then French (Gallimard)  then English (Nlb 1971). The English version is the most complete I would guess.
Comment: My interest in this is that we have almost forgotten that reason may need ends, and for instance things like science can end up doing more harm at times than good. However, that is not what the book is precisely concerned with. Velkley says Kant early on was interested in the perplexity over the question of the place of reason in human life....human good, social and individual and goes on to make the case that Kant was influenced by Rousseau. I'll stop there, this is already long.
Answer: An interesting question. Kant's definition of philosophy as "the science of the relation of all knowledge to the essential ends of human reason" raises some questions. For one, it would be natural to think that knowledge is the end (that is, the goal) of human reason, or at least one of its primary ends. But here Kant speaks as if the ends of human reason are beyond knowledge itself. What can they be?
I think that Kant's definition relates to his unique distinction between the cognitive faculties which he calls reason and understanding, a distinction which is one of the founding principles of the Critique of Pure Reason (CPR). Structurally, the understanding is discussed in the "analytic" part of CPR, which deals with what we can know. And reason is discussed in the "dialectic" part, which deals primarily with what we cannot know, but that we have an almost irresistible urge to believe that we can know.
So what are the ends of reason? Kant attributes to reason two interrelated ends. First, reason demands the completeness of knowledge, and cannot rest with merely partial accounts. Second, reason demands to know the unconditioned, the first principles and causes, and cannot rest with knowledge of principles and causes which need further explanation, further justification, etc.

The transcendental conception of reason is therefore nothing else than the conception of the totality of the conditions of a given conditioned. Now as the unconditioned alone renders possible totality of conditions, and, conversely, the totality of conditions is itself always unconditioned; a pure rational conception in general can be defined and explained by means of the conception of the unconditioned, in so far as it contains a basis for the synthesis of the conditioned. (CPR, "Of Transcendental Ideas.")

In the "dialectic" part of CPR, Kant tries to show how, on the theoretical side (as opposed to the practical side) reason's high hopes are doomed to be frustrated. Our attempts to know about God, about whether the world was created or not, and other big questions, could never be satisfied. On the positive side, reason can guide our researches in the domains that we can know, and reason can guide us in ethics, the practical domain. And it is reason itself that reflects on itself and is bound to get to those conclusions.
So when Kant defines philosophy as "the science of the relation of all knowledge to the essential ends of human reason" he alludes, I think, to the above mentioned two ends of human reason: completeness of knowledge, and knowledge of the unconditioned. It is these two aims, their fulfillments and their frustrations that, according to Kant, it is up to philosophy to investigate.

Kant on the Essential Ends of Reason


Unable to mount home-directory for user after fresh install 14.04

Question: I performed an fresh install of Ubuntu 14.04. I have /home on a different partition from root. Installing 14.04 and mounting /home went without any problem. During installation I was asked to make a user and I made a new user with my user-name and password. My home folder was correctly added to my user-name. After this I made users for my different family members and adding their existing home folder which went fine except for one.
In one case I could make the new user, same user-name as the home folder. Login for this user failed. The screen turns black and one would expect the desktop for this user to appear. I can hear the drum-sound which indicates that you are logged in, but the login-screen returns. I am unable to login for this one user.
If I try to login this user in cli everything is fine. I can browse the home folder and files.
Of course I don't want to loose the home folder for this user. What should I do?
Thanks in advance.
Comment: It's possible that the user that you are having problems with has a different UID than before.
Answer: Elder Geek is right about the UID.
The steps to check the problem goes like this:
<code>$ cd /home/[user-name]
$ ls -la
</code>
You might see the UID is appeared as number rather than your current user name, e.g. appear as 1002
<code>drwxr-xr-x  2 (1002) ...bla bla... 40 Mei  22  2014 Documents
</code>
You can check your current user UID
<code>$ cat /etc/passwd | grep [user-name]
[user-name]:x:1000:1000:[user-name] ...bla bla bla
</code>
If they are different (1002!=1000) than we know this is the problem.
Solution:
<code>$ chmod -R [user-name]:[group-name] /home/[user-name]
</code>
You may now try to login.
Cheers : )
Answer: I had similar problem afer installing caffeine. /home/username directory was not present. I created directory and could log in.


Is it possible to see option prices from the past?

Question: For example, I can look up what a companies stock price was like in the past, but I can't look up an option chain from the past.
Answer: Yes, past option prices are available for many options, but as far as I know not for free.  You can get them from, for example, OptionMetrics.  Probably there are other providers as well, which may be cheaper for an individual or small institution.
OptionMetrics data comes from the National Best Bid and Offer.  Probably there are some over-the-counter options that are not included here, but for someone asking this question, OptionMetrics will most likely have the option you are interested in.


13 year old daughter refusing to wear a real bra

Question: My 13-year-old daughter has a training bra that she has been wearing 24/7 for almost 2 years now. When we first got it, it was her first bra and she has only tried on one bra when I got her fitted. I bought her lots of bras over the years but she will not wear them. She is struggling to get the bra on as her breasts are so much larger than the training bra is meant for. The last time I got her fitted she was a 34b cup, The training bra is meant for small busts let alone a 34b cup. I have no idea what to do.
Comment: Have you asked her, why she refuses?
Comment: @Marzipanherz I was thinking along the same line, hence my question. First rule when clothing a teen: Get their input. >.<
Comment: Hi, and welcome to parenting.SE! There is some information missing from your question: Why do you think this is a problem? And what does your daughter say? Please edit your question to add this information.
Comment: "_I bought her lots of bras over the years_" Does this mean you went shopping on your own, or did she join you? If she didn't pick them herself, maybe she simply doesn't like them? Could she feel ashamed of telling you what she would like?
Answer: It's entirely possible that she is uncomfortable with the changes in her body. Perhaps she would feel more confident in a sports or athletic bra? It may "hold her in place" more securly and allow her to run and play without drawing the attention of boys her age.
Answer: In the end, she has to wear the bra and feel comfortable in it, so you should get her input / feedback. Don't just go shopping for bras on your own, but take her with you. While you can also suggest bras for her, let her choose some herself. Grant her freedom in choosing ones she likes. You can then sort out some bad choices and let her try on the rest.
This has the following benefits

You keep control (e. g. if she chooses too expensive or really inappropriate ones (like too sexy ones))
You learn more about what she wants / needs, even without her having to say a single word, just by letting her explore freely and see what she presents you
If she really refuses to, it's a good starting point for a discussion (listen to her, let her explain)

While you shouldn't allow really inappropriate ones, still respect her choices as long as they are still sensible and an improvement (she has to wear it, not you). She may feel insecure, as this is a crucial step in her development, so you could make it easier for her by

Having someone else go shopping with her, whom you both trust (e. g. an older sister), but be sure she also trusts them and they have a good relationship
Maybe not just go shopping for bras exclusively, but also for other useful itmes (so it's just mother and daughter going shopping, not the huge bra shopping event)

You could also get her input without going shopping, by asking her about it (like above, a trustworthy third party is also a possibility). The purpose should be to find out what she wants, so it should be comfortable for her and not, for example, be accusatory ("I bought you all those bras, but you...!").
After all, you don't know why she acts that way yet, and if she is anxious or insecure, for example fearing teasing, pressure would rather make it worse. She should feel comfortable opening up to you and not get punished for doing so. Make it a win-win situation for you both, so no negative consequences - it's about solving the issue, i. e. her getting an appropriate bra you both can agree with.
Answer: Please do get her input, as that is critical.  After talking to her, she may be open to sports bras, and if so, then go shopping with her or give her the money and drop her off while you wait in the car if going shopping with you is embarrassing to her.
MY daughter is around the same age and should wear bras as well, but often goes without.  When she does, it is either a sports bra or something sexy that she picked out on her own, depending just what she is doing, but she finds the sports bras to be more comfortable for her.
Answer: This is not that unusual at that age—it's mortifying to be aware that this is something your parents are thinking about, and mortifying to be dealing with body changes.
Have you asked her if she'd be comfortable with bralettes or bra tops sold at a place like Aerie, or  something like an athleisure crop top (like this)? Similar to the sports bra suggestion above, something like a CK bralette would potentially be a good fit. They look athletic, similar to most training bras, and basically read as slightly more constricting tops—not bras, which feel adult and slightly mortifying. If she has a sporty style anyway, a matching set in the form of an athleisure top and leggings or bike shorts will solve the problem, anyway.
If your main concern is just making sure she's not wearing something so small that it will hurt her, a flexible sports bra or bra top seems like it might be better received.
If none of that works, you might see if she'd be receptive to going shopping with an older sister, aunt, friend's mom, etc.—someone who reads as an older peer rather than a parent. She may be less embarrassed that way.


What do we learn from training a dataset for logistic regression

Question: What do we learn from training our dataset in Logistic Resgression?
Like in Linear Regression, with the help of training set we are able to generate a best fit line(y = mx+c) where m and c come from training our dataset.
Similarly, once we train our model for logistic regression, what is that the model learns which is then used to predict a class for a particular input?
Answer: I hope this is what you are looking for:
In Linear regression, the parameters are learned (e.g. theta1,theta2, etc.) which are then used to help us in predicting the real value ( as it is the regression problem)
But In case of logistics regression (as it is used for classification purposes) the same parameters are learned but different activation function is used like sigmoid which results in the range of 0 to 1( which actually shows the probability of an outcome). So, based on your requirement, if the result of the sigmoid or any other activation function crosses a certain threshold value which can be any between 0 to 1, then it is classified as one class otherwise the other class.
For example, If after multiplying all the parameters and input values and then applying activation function on the multiplication result, the output value is 0.7 which let say is great than our threshold value(e.g. 0.5) then it is classified as YES otherwise NO.
Comment: Let me know if you want to know anything else. I would be glad to help you out.
Comment: Thanks Faizan. From what I understood, we still predict a y value like we did in regression and then pass that value through an activation function and then it maps to a probability value. I would want to know that when solving classification problem, training dataset only has labels in the prediction(y_train) column, whereas in regression problem,the prediction value would have continuous values which would help obtain the necessary parameters. How are those parameters obtained for logistic regression for we only have labels in dependent variable?Please excuse the naiveness as I'm a beginner
Comment: By parameters, I mean slope and intercept.
Comment: Well if your concern is that how categorical labels are treated during the process then Label encoding or one hot encoding is used to convert the label into numeric values... continue
Comment: Here is the link where you can see how encoding is performed https://www.google.com/amp/s/machinelearning-blog.com/2017/12/27/266/amp/


Can elliptic curve point common factors be detected?

Question: Consider the two EC points $X=abG$ and $Y=bG$. Is it possible for someone to examine $X$ and $Y$ to determine if there is a common factor, as long as $a$ and $b$ are randomly chosen numbers between 0 and the size of the finite field? Even if the common factor $b$ cannot be determined, can it be determined if there is, or if there is likely to be a common factor? Assume the ed25519 curve is being used.
Comment: Don't forget to upvote questions guys, we're slacking.
Comment: Assuming [this topic](https://github.com/monero-project/research-lab/issues/7#issuecomment-280540193) is the interest of this question, shouldn't a more relevant question be as follows: with fixed $a$ and random $b_i$ for $i=1,2$, and $Y_i=b_iG$ and $X_i=aY_i$, is it possible for an observer to find a link between the two pairs $(X_1,Y_1)$ and $(X_2,Y_2)$ by somehow figuring out that each $X_i$ is a multiplication of $Y_i$ by the same $a$ even though he couldn't know $a$ itself? I hope the answer is no :)
Comment: @MaartenBodewes I'm sorry? When did upvoting questions become mandatory?
Comment: @fkraiem Never, but as mentioned before on meta, it's a bit strange that a well asked question doesn't receive any upvotes - not even by the person answering it. And, truth to be said, I often forget as well (especially when I'm focussed on answering). But if you don't think the question is worth an upvote then don't; this was just a friendly *reminder* to upvote good questions. Truth to be said, I think we're a pretty well organized Q/A site, but this we can do better.
Answer:
Is it possible for someone to examine $X$ and $Y$ to determine if there is a common factor, as long as $a$ and $b$ are randomly chosen numbers between 0 and the size of the finite field?

(Actually, you mean the size of the group)
Technically, the answer is "yes, it is easy to determine that".  The easiest subcase is if $G$ (and hence $X$ and $Y$) belong to the large prime subgroup of x25519; then the rule is "unless Y is the point-at-infinity and X is not, the answer is "yes".
That is, there will always be an $a$ such that $X = aY$.
It's a little trickier if $G$ generates a larger subgroup, but it is still easy (it might take a little computation on the attacker's part).
Of course, the fact that it's always true (whether or not you consciously generated such a relationship between $X$ and $Y$) means that the attacker can't deduce anything from that information.
Comment: Thank you - just to clarify, you're saying there is no way that the common factor $b$ can be determined?
Comment: Well, we certainly hope lot.  That's the discrete log problem, and if someone can solve that, well, essentially all crypto on elliptic curves is broken...


Which is better lockup or non lockup converter?

Question: So which is better a lockup converter or a non lockup. It's being put in a Chevy 4x4 with a 700R transmission, it's a daily driver and used for towing?
Comment: Lockup converters are almost universal, is this an academic question or are you being given a choice?
Answer: If you are going to be towing, you want a lock-up torque converter. Heat is the bane of transmissions. Towing will add heat to the transmission. A non-lock-up torque converter will add more heat. With a lock-up when you get to speed, the torque converter will lock-up, which creates a direct drive from engine to transmission. No additional heat will be added into the tranny fluid due to slippage during operation. This will help extend the life of the transmission.
You'll also want to consider putting a large external tranny cooler on your vehicle. This does two things. The obvious one is keeping the transmission cooler. The second thing it will do is adding more transmission fluid into the mix, which will usually allow it to last longer. The transmission cooler which is located in the coolant reservoir is not up to the task. Bypass this all together as it will not provide any additional cooling which the external one won't cover.
Answer: The 700r will only lock in 4th gear. This can be hacked for towing to manually engage in 3rd, where most heavy towing is done. http://www.hotrodders.com/forum/700r4-3rd-4th-lockup-102313.html
Answer: The main reason lock-up torque converters were introduced was for "parity" with manuals to try to match or, at least improve, the fuel consumption when cruising.
This was also combined, in some cases, with an "overdrive top" again for the cruise performance and the top end speed.


What's the most elaborate ancient mechanism?

Question: I'm playing the latest installment of the Tomb Raider, where you uncover secrets of ancient Incas and Maya. The game is full of huge stone doors that open only when you go through an elaborate sequence and so on. It's pretty obvious to me that what's portrayed in the game is an artistic exaggeration, but it led me to wondering about the elaborate mechanisms that did in fact exist. Now, I'm mostly interested in large and even gigantic mechanisms, but if you have anything interesting of the Antikythera's size, feel free to share too.
Comment: Welcome to History:SE. Questions which attract answers based primarily on opinion are expressly off-topic on this site.  You might find it helpful to review the [site tour](https://history.stackexchange.com/tour) and [Help Centre](https://history.stackexchange.com/help) and, in particular, [ask].
Comment: How do I compare the "elaborateness" of two mechanisms?
Comment: Number of moving parts, the size and importance of the task, etc. Academic discussion is now what I had in mind, this is more of a pop-science question. Within reason use whatever measure that leads to an interesting (in your personal opinion) example.
Comment: @Mark C. Wallace: Aqueducts weren't quite continent-spanning, the longest being in the neighborhood of 500 km: http://www.romanaqueducts.info/aquastat/aquastatlength.htm  OTOH, would you consider a road system to be a mechanism?
Answer: One has to distinguish the things for which we have direct archaeological evidence,
the things which can be reliably reconstructed from literature sources, and the things which are mentioned in the literature but with inadequate description such that we have no idea how they really looked.
To the first type belongs the Antikythera mechanism.
Examples of second kind are artillery pieces, and various machines described in
the book of Heron.
Examples of the third kind are Archimedes planetarium and especially the enormous warships of Hellenistic era. See, for example,
Leontophoros,
Tessarakonteres.
All these things belong to the Hellenistic epoch.


Does C64 /DMA assertion immediately disconnect the CPU from the address bus?

Question: I have heard several claims (in the comments on this question and
answers) that asserting the D̅M̅A̅ signal on the Commodore C64
cartridge port will immediately take the CPU off the bus by deasserting its
AEC line. How does it do this?
Comment: If it's any consolation, the TRS-80 effectively does the same thing. If you try to assert the BUSREQ pin, the logic tri-states out all of the CPU busses immediately, rather than waiting for the BUSACK signal telling the requester that the Z80 has, indeed, given up the bus. In fact, the BUSACK signal isn't even made available anywhere. Good times.
Answer: In all versions of the schematics from the Commodore C64/C64C Service
Manual, the D̅M̅A̅ line proceeds from the cartridge port to:

A 3k3 pullup resisistor.
A 74LS08 AND gate with BA (a VIC signal) to CPU RDY.
A 74LS08 AND gate with "system" (i.e., not CPU) AEC generating CAEC
to the CPU's AEC pin.

Thus bringing DMA low will immediately bring low one side of the AND gate
in 3 above, causing the output to be low and AEC to be deasserted on the
CPU. (The VIC-II chip may also independently deassert CAEC from the other
side of the gate; this is used for DRAM refresh, among other things.)
The implication here is that unlike just asserting RDY, which can safely
be pulled low any time,¹ one must be very careful of timing when asserting
D̅M̅A̅. The "deassert RDY and wait three cycles" strategy to avoid
conflicting with CPU write instructions isn't available here; you must keep
track of when the CPU is doing a write and avoid asserting D̅M̅A̅ during
that time lest it disconnect the CPUs address lines while it's completing a
write sequence.

¹ CSG NMOS 6500 Microprocessors (1985) data sheet, p.7: "If
Ready is low during a write cycle, it is ignored until the following read
operation."
Comment: One may safely use the approach of driving RDY low and assuming the CPU will release the bus within three cycles, *but one would need to refrain from asserting /DMA during those three cycles*.
Comment: At first I though the two illustrations of 74LS08 gates were of the gates for points 2 and 3, but they're actually two examples of the third point (from different schematic diagrams).
Comment: @cjs: Hmm... I guess I'd blindly assumed an external wire would be available to trigger RDY.  A lot of bus connectors seem to make some curious decisions.
Comment: @supercat Not on an (unmodified) C64, as far as I can see. The only connection to the CPU's `RDY` pin is the output of the gate in connection 2, which can only be brought low by asserting `D̅M̅A̅`, which will also disconnect the CPU's address bus per connection 3. (`BA` is connected to the other input of the gate in connection 2, but that's an output from the PLA.)


Discrete wavelet transform disadvantages

Question: I read in a paper that the  discrete wavelet transform (DWT) has two disadvantages
The first one is the shift variance property due to the downsampling process. Could you please help me understanding why downsampling leads to shift variance?
The second disadvantage is the lack of directional selectivity.  Why does DWT lacks directional selectivity?
Comment: If we are lazy and use separable transform on rows and columns then we get bad directional sensitivity. Actually, the cartesian sampling grid in itself is a pretty poor choice for directional sensitivity. We can build real 2D wavelets on more suitable grids to solve this.
Comment: Can you please provide a link to the paper?
Comment: [link]
(https://books.google.com.eg/books?id=49FBDwAAQBAJ&pg=PA79&lpg=PA79&dq=DWT+shift+variance+property+due+to+the+downsampling+process+lack+of+directional+selectivity.&source=bl&ots=wnhZpeTQcY&sig=ACfU3U3heH_2sefjO995Jqn52pJ7udyrug&hl=en&sa=X&ved=2ahUKEwjtqtG9xZnlAhUAD2MBHb-FAC8Q6AEwBHoECAkQAQ#v=onepage&q=DWT%20shift%20variance%20property%20due%20to%20the%20downsampling%20process%20lack%20of%20directional%20selectivity.&f=false)
@A_A
Answer: A $2$-channel stage of a wavelet transform, combines two filters in parallel, followed by a down-sampling by two. The later is the cause for shift-invariance, as the filters are time-invariant. Signals $$x_0[n] = \{\ldots,0,1,0,1,0,1,\ldots\}$$ and  $$x_1[n] = \{\ldots,1,0,1,0,1,0,\ldots\}$$ which are shifted by only one sample, yield respectively  $$y_0[n] = \{\ldots,0,0,0,0,0,0,\ldots\}$$ and $$y_1[n] = \{\ldots,1,1,1,1,1,1,\ldots\}$$
Answers to down-sampling a thus not shift-invariant. This happens even with low-pass or high-pass filters. In an $L$-level wavelet decomposition, the overall wavelet filter bank is invariant to multiples of $2^L$ shift, not the intermediate one.
When applied in 2D, classical wavelet schemes, by simplicity, apply 1 DWT on rows and columns of the image, in a separate way. The resulting 2D wavelet filter is of rank one, very poor at separating directions other than vertical or horizontal. However, genuine 2D wavelets with better  directional selectivity exist. The paper A panorama on multiscale geometric representations, intertwining spatial, directional and frequency selectivity, Signal Processing, 2011, is devoted to that topic.


Should the 'configuration' tag be nuked from orbit?

Question: It's on 788 questions, but I can't imagine where it'd have a valid use.  Should configuration perhaps just be silently nuked in the database and blacklisted?
Answer: By definition everything that is posted on SF deals with configuration in one way or another. I can't think of a single valid question that can be asked about hardware or software that doesn't fall under the configuration umbrella. I'd say nuke it.
Answer: Configuration does seem like a meta tag, similar to security or performance, which describes an aspect of a problem, rather than the specific things the problem involves. Personally, I class it in with the likes of security as an allowable meta-tag.
Comment: Based on the general principle of "could this be the only tag on a question and still make sense?", I don't think that [tag:security] is in the same class as [tag:configuration].


Python local folder path for each platform

Question: My script works in special folder, which name is "Fold".
On the different computers and operation systems path to this folder is different.
For example, on Mac it will: "/Users/user/Fold". On Windows - "C:\Users\user\Desktop\Fold" .
How I can input the path to this folder in my Python script for working on each platform? What should I type inside my script, if the script works only inside "Fold" folder?
Comment: `Desktop` does not fit the theme. You'll have to special-case it if you insist on it. It would, however, make more sense as `c:\Users\user\Fold`, `c:\Users\user\AppData\Fold` or `c:\Users\user\Documents\Fold`.
Answer: the os module has the functionality for identifying various operating systems
in your code you can do this
import os

if os.name == 'nt'
    # do something nt stands for windows
    path = 'C:\Users\user\Desktop\Fold'
elif os.name == 'posix'
    # linux or mac
    path = '/home/user/Desktop/Fold'

the platform module gives more details than the os module the os might return posix for both linux and mac on my linux machine platform outputs this
import platform

>>> print(platform.system())
Linux
>>> print(platform.release())
3.13.0-76-generic

platform.system() should return 'Darwin' for mac
Answer: You can use
import sys
import os
sys.platform == "win32":
    fold = os.path.join("C:", "Users", "user", "Desktop", "Fold")
elif sys.platform == "Darwin":
    fold = os.path.join("/Users", "user", "Fold")
else:
    ...

Or you can setup an environment variable on each computer if it changes within a same OS.
Answer: You can get the path to the user folder (Mac: /Users/user, Win: C:\Users\user\) via os.path.expanduser("~"). From there, your implementation seems OS-specific - maybe only the Windows-implementation places its data on the desktop. Since you can get the platform identifier via sys.platform, you could do something like this:
import sys, os
folderPath = os.path.join("Desktop", "Fold") if sys.platform == "win32" else "Fold"
fullPath = os.path.join(os.path.expanduser("~"), folderPath)

If you want to use the path to the desktop folder on other systems, please refer to Cross-platform Desktop directory path?


Is Sanskrit really a divine language or is it simply the common spoken language of the Vedic era?

Question: If Vedas were to be "heard" in the medieval era by the sages, I am sure they might have composed it in Awadhi or some other common language, as even Tulsidas composed.
Comment: Traditional Sanskrit grammarians treat it as a divine language. Modern day linguists treat Sanskrit as just any other language.
Comment: Yes, it is of divine origin. It's a bit roundabout to say Vedas are in Sanskrit. Instead, Vedas are Sanskrit. Vedas are not composed by any human. They are Apaurusheya (not of a man). Sanskrit itself came from the sounds of Shiva's dumroo. Panini simply expounded on its grammatical rules through sutras. He didn't invent Sanskrit.
Comment: The difference between Sanskrit and other languages is that Sanskrit is eternal, because it is the language of the Vedas, and the Vedas are eternal.
Answer: As C. V. Vaidya says in the History of Sanskrit Literature, Vedic Sanskrit is simply the language spoken by the common people during the Vedic period.

THREE PERIODS
Macdonell divides the history of Sanskrit literature into two periods,
  the Vedic period and the Sanskrit period. But it is more proper to
  divide the history into three periods, the Śruti period, the Smṛti
  period and the Bhāṣya period, as we propose to call them. The
  language of the Vedic literature can be given no other name than
  Sanskrit, the Indo-Aryans brought with them into the Panjab a branch
  of the language of the ancient Aryan people which may properly be
  called, by distinction, Sanskrit. This name no doubt arose later when
  the Prakrits came into being, by way of opposition, meaning the
  language of the refined people, as opposed to Prakrit, the language of
  the common people. But that name has to be carried back to the Vedic
  times. If Sanskrit is a name which is to be confined to the language
  of Patañjali's days, Vedic literature cannot come within the range of
  a history of Sanskrit literature. We may call the Vedic language Vedic
  Sanskrit, the language of the days of Pāṇini post-Vedic Sanskrit, the
  language of the days of Patañjali classical Sanskrit and the language
  of the days of Śaṅkarācārya and after modern Sanskrit. The language
  is the same throughout this length of time, though it has different
  aspects in these four, rather three, periods, just as English has been
  divided into old English, Elizabethan English, and modern English. It
  is needless to state that the identity of a language continues so long
  as its grammar remains practically the same.
The Vedic people actually spoke this Sanskrit language in the form it
  then had and the Vedic singers did not use an artificial language for
  their poetry as is sometimes supposed. There was, in the beginning, no
  Śūdra caste, the Aryans being homogeneous; the cultivators, the
  warriors and the priests, being of the same Aryan race, were of the
  same mental and physical capacities. There was then a slight
  difference between the spoken language of the common people and that
  of the higher class people, such as exists in every country and at
  every time. The language of the Vedic common people must, however,
  still be called Vedic Sanskrit; and it is interesting to find that
  when the Aryans migrated to the Deccan, they carried words of this
  Vedic Sanskrit, some of which still survive in the language of the
  common people of the Deccan. The pronoun tyo, used by common people,
  instead of to used by higher classes in Maharashtra, is a survival of
  the tyas of Vedic times. In short Vedic Sanskrit was a spoken
  language as well as post-Vedic Sanskrit of the days of Pāṇini. The
  language had changed visibly by this time; but it was still the same
  language and Pāṇini gives no separate grammar for Vedic Sanskrit, but
  simply marks certain peculiarities of the language as used in the
  hymns. He always makes the simple distinction bhāshāyam and
  chhandasi where there are differences. The word bhāshāyam used by Pāṇini clearly proves that it was a spoken language of which he
  wrote the grammar and that the name Sanskrit had not yet arisen, nor
  of course, Prakrit.
...
For these reasons, therefore, it would be appropriate to divide the
  history of Sanskrit literature into three periods; viz., the Vedic and
  post-Vedic period (c. 4500 B. C. to 800 B. C.) to be called the Śruti
  period, the classical period (c. 800 B. C. to 800 A. D.) to be called
  the Smṛti period and the modern period (c. 800 to 1500 A. D.) to be
  called the Bhāṣya period. In the first period, Sanskrit was spoken
  by all people who were chiefly of the Aryan race; in the second, it
  was spoken by the high class males while their women and lower classes
  spoke the ancient Prakrits which were only softened Sanskrit; and in
  the third period Sanskrit was dead as a spoken language. Naturally the
  literatures of the three periods differ in language — easy and simple
  in the first, polished and refined in the second and artificial and
  pedantic in the third. Then again in the first period, literature is
  chiefly religious and philosophical and at once became sacred. In the
  second period literature is highly thoughtful and has become
  quasi-sacred or authoritative, where not religious, and in the third
  period literature becomes scholastic though usually full of powerful
  reasoning and forceful expression.
Answer: Rig veda 1.164.39 says as follows:

रचो अक्षरे परमे वयोमन यस्मिन देवा अधि विश्वे निषेदुः |  यस्तन न वेद
  किं रचा करिष्यति य इत तद विदुस्त इमे समासते ||
ṛco akṣare parame vyoman yasmin devā adhi viśve niṣeduḥ |  yastan na
  veda kiṃ ṛcā kariṣyati ya it tad vidusta ime samāsate ||
The vedas rest in the imperishable syllable - OM (ॐ) - in the
  Supreme ether (of the heart). Those who do not know that, what can
  they do with the veda? Those, who know that are gathered here

Aksara - अक्षर  means imperishable.  That which is imperishable is DIVINE.  It was first made known to mankind through Sanskrit language.  So Sanskrit is DIVINE.
While quoting the statement from Abrahamic Text "In the beginning was the Word and the Word was with God ", Swami Vivekananda said that the Word is the Vedas, and Sanskrit is the language of God. God spoke once. He spoke in Sanskrit.


Upgrade to final from Public Beta?

Question: I'm currently on the public beta of El Capitan, how do I upgrade to the final version of the new OS?
Answer: You don't need to upgrade. OS X 10.11 GM and final release are the same according to Apple and once 10.11.1 is released both the GM and final release will update to it.
Answer: The safe way:
Boot into Recovery HD, erase the drive, and restore from your Yosemite backup (if you have one). Then download the installer and upgrade.
I wouldn't recommend just downloading the installer and updating, as bugs could be carried over.

Upgrade to final from Public Beta?


Convert CMYK into K only

Question:
Using InDesign I created the interior of a 352-page book. It is supposed to be black only. But some of the diagrams in the book have hidden CMYK values.
I created a PDF from InDesign. The PDF retains the hidden CMYK values.
How can I convert my PDF into one that is black ink only, with no CMYK or color values? Is there a simple way to do this in Acrobat?
Answer: Can do:

Tools -> PDF Standards -> Preflight -> Convert to Grayscale

or

Tools -> Print Production -> Convert Colors -> Conversion Profile -> Pick the one you want
Comment: I would check after if the values are converted to K100%.
Comment: Thank you! This Preflight > Convert to Grayscale is by far the easiest.
Answer: Ideally, you would alter the images placed in InDesign using their native applications - Photoshop/Illustrator -  then replace them (or update the links to them) in the InDesign layout and regenerate the PDFs needed.
Conversion to Grayscale from CMYK can often result in various percentages of black and rarely will result in 100% black if that's the desired percentage. The only way to ensure 100% black is 100% black is to make certain the original artwork is set to use that color and percentage.
Comment: While that's a good rule for quality, it won't necessarily result in a grayscale PDF. Complete grayscale is often required in to avoid color clicks on the printer. So, even if Wernermischke were to go through the trouble of converting his images to grayscale, it would be useless if production required trim marks or page information, which appear in Registration black, which would trigger the color click. The most sure-fire way to prevent unnecessary color clicks is to somehow generate an entirely grayscale PDF, OR (if the RIP supports it) to configure the print job to run in black only.
Comment: Marks are irrelevant. I suggested altering the **original images** not the PDFs In *most instances* converting CMYK to greyscale results in a tint of black. Which is fine if that's what you want. But if your desire is to get 100% solid black, converting from CMYK to grayscale will almost **never** accomplish that.
Comment: I disagree. Marks and page info are perfectly relevant considerations if the goal is to prevent color clicks. Registration black is not simply 100% black, but 100% of all colors. So converting the source images to grayscale will result in the best quality output, but unless the PDF is ALSO exported to a grayscale format (or converted later) the machine will often still record a color click due to the trim marks and/or page info.
Answer: You can do this really easily by using the preflight option in Acrobat.
In the 'Prepress, Colour and Transparency' fixes menu, search for 'Correct 4C Black' - this will identify any 4C black in your document and then change it to 100% K
You can specify if it's text and vectors, vectors, just text, images, etc. you want changed as well, which is great.
Comment: Hello HLK, welcome to GD.SE and thanks for your post! If you have any questions about the site or the Stack Exchange model in general (gist: we are not a forum, but a Q&A site), have a look at the [tour](https://graphicdesign.stackexchange.com/tour) and the [help]. Do stick around and have fun here!
Answer: You don't have to do it as an extra step in Acrobat. You can create the PDF in grayscale to begin with by "printing" to the Adobe PDF driver with "Composite Gray" selected in the Output tab of the Print Dialog.
Comment: The Adobe PDF driver died in roughly 2002. No user in the past 12 years has had the Adobe PDF printer drivers installed. While this answer was valid a decade ago, it's invalid at this time.
Comment: While one may have access to the latest release of CC and Acrobat, many still use Acrobat X, which installs the PDF printer driver. So it's not quite so old as that. Many of us with heavy investments in plugins hang on to legacy versions of the host platform in order to mitigate the cost of upgrading for no significant benefit. It's not at all uncommon for users to be running vintage releases for perfectly legitimate reasons.
At any rate, it doesn't have to be the Adobe PDF printer. There are free contemporary pdf printer apps out there that could easily accomplish the same effect.
Comment: Acrobat X does *not* install the PDF driver. The last version to install that driver was Acrobat 8 I believe (may have been 7 or 9 though, definitely not Acrobat X.) While you *can* manually install the driver. It is notoriously old and problematic, which is why Adobe dropped it.
Comment: Thanks for the correction. However, as I said, there are contemporary PDF printers available that can accomplish the same goal.

Convert CMYK into K only


Is focal length of a planoconvex lens twice to the focal length of equiconvex lens from which the planoconvex lens was made?

Question: If an equiconvex lens is divided equally, we will obtain a planoconvex lens. Let assume focal length of our equiconvex lens is 'f'. I would like to know what will be the focal length of planoconvex lens that we obtained after dividing equiconvex lense. Will it be twice of 'f'? Or will it be 0.5 of 'f'? How to determine it?
Comment: Just think about the refraction and the resulting deviation of light at each face of the two types of lenses.
Answer: Using the Lens-Maker's equation:
$$ \frac{1}{f} = \frac{n_{lens} - n_o}{n_o}\left(\frac{1}{R_{left}}-\frac{1}{R_{right}}\right)$$
And because we have an equiconvex lens, $R_{right}=-R_{left}$ (the negative sign is from the sign convention of the equation), so we have:
$$ \frac{1}{f_{equi}} = \frac{n_{lens} - n_o}{n_o}\left(\frac{1}{R_{left}}+\frac{1}{R_{left}}\right) = 2\frac{n_{lens} - n_o}{n_o}\frac{1}{R_{left}}.$$
So $f_{equi}=\frac{R_{left}n_o}{2(n_{lens} - n_o)}$ and for the planoconvex lens, $R_{right} \approx \infty$ so the equation becomes:
$$ \frac{1}{f_{plano}} = \frac{n_{lens} - n_o}{n_o}\left(\frac{1}{R_{left}}+\frac{1}{\infty}\right) = \frac{n_{lens} - n_o}{n_o}\frac{1}{R_{left}}.$$
So when you cut the lens in half, the focal length is actually doubled when you cut the lens, since $f_{plano}=\frac{R_{left}n_o}{n_{lens} - n_o}=2 f_{equi}$.
For more info on the Lens-Maker's equation, you can look here for an explanation.
Answer: Focal lengths are first order properties of lenses. An equi-convex lens is ideal for imaging an object 2*focal length away and forming an image 2*f behind. If you cut the equi-convex lens right down the middle such that you get a convex-plano lens, the focal length will double and it will basically collimate the object that was originally 2*f away. Shape factor can be changed while keeping the focal length a constant and you can watch the spherical aberration change as a function of shape factor for a given f. But that's another story. Bottom line, I agree with first answer. Focal length will double.


OpenGL vs DirectX difference from Graphics card perspective?

Question: I want to know the difference in purely hardware level if there is any. For example the most simple question: Is there a chip for DirectX and another chip for OpenGL? What do hardware producers do to make their cards DirectX or OpenGL compliant?
Answer: No, OpenGL and Direct3D are both APIs that abstract the functionality of the actual hardware. Direct3D is a Microsoft application and standard while OpenGL is an open standard.
Any GPU will work with OpenGL and Direct3D as long as there's a driver for it. The driver is what takes Direct3D/OpenGL calls and does all the really low-level interfacing with the GPU. There is no "DirectX only" GPU and no "OpenGL only" GPU, unless for some strange reason the drivers only support one of the APIs.
From the graphics card's perspective, it's only communicating with the driver. The driver then communicates with all the APIs it supports.
Hardware vendors must write drivers against the Direct3D and OpenGL specifications in order to make their cards compliant with that API.
EDIT
If you're looking for some differences in the two APIs, DirectX is more geared towards games while OpenGL is a more general 3d rendering platform. More on that in the Wikipedia article comparing the two.
Comment: There are new features in DirectX 11/OpenGL 4 that need the graphics card hardware to be wired up in a certain way. It's the exact reason why OpenGL 3.3 exists, as a way to let older graphics cards support the OpenGL 4 features that weren't dependent on a change in the hardware. For example, a graphics card from 1995 wouldn't be able to execute any shaders because it's built for a fixed-function pipeline. The programmable pipeline made it so that GPUs needed more general cores instead of very specialized ones.
Comment: @SRN It does in backwards compatibility mode. OpenGL 3.3 works on cards released before 2010 as well. If you want to use new features then of course it won't work.
Comment: then why directx 11 does not work on directx 10 cards
Comment: The hardware may require some minor extra hardware features to support both. For example, texture coordinates are upside down in OpenGL, compared to D3D. Clip space coordinates are also different.
Answer: Direct3D and OpenGL are APIs, they're implemented in the drivers by the manufacturers. For OpenGL, the manufacturer has to implement a set of functions that act in a way described by the specification provided by the Khronos Group. Then the programmer can retrieve the addresses to those functions and use them in the program, the details are OS dependent, it's usually done in C or C++ sine that's what OS APIs mostly use. OpenGL doesn't care how much RAM your graphics card has, so to speak. Direct3D has a more manufacturer friendly philosophy behind it, Microsoft gives more leeway, but it's still just a matter of drivers.


Hostname bindings for IIS in Sitecore Azure PaaS

Question: For Sitecore Azure (up to 8.1) how are the hostnames configured for Azure PaaS CD environments? Is this something which happens automatically based on settings found in Sitecore.config/Web.config?
Answer: You need to configure the hostnames in the portal (or via PowerShell) first. This will involve a DNS validation step so you will need access to your DNS provider as well.
You only need hostnames in the Sitecore Config if your system needs to differentiate site content between several domain names. If it's just the one, you only need to configure the Azure website.
PS Azure Website-grade PaaS is only officially supported from 8.2.1  Be careful when running multiple instances as there are Sitecore components that use the file system for storage and Azure PaaS had a shared filesystem across instances.
Comment: This answer was downvoted but nobody bothered to leave a comment as to why.  Clearly someone doesn't agree my statements (from 2 years ago) - it would be very helpful to future visitors if you identified _in what way_ the above is incorrect, not relevant or off topic. I don't have the rep to see who downvoted, but you know who you are.  Having re-read the answer, it still seems right to me, with the possible exception that you don't *have* to configure hostnames first, you can configure them at any time really, it's just you have to configure them before you can use them obviously.


Can a passport-less person (Indian origin) in Saudi Arabia travel?

Question: They were born in Saudi Arabia but for some reasons their passports were never made. They were on their mother's passport earlier as kids who was a Pakistani (she has passed away) . Now they are 18+ of age and have applied for an Indian nationality as father is an Indian. Waiting for 5 years now. Can they travel anywhere?
Comment: Not having a passport ≠ being stateless.
Answer: They might manage to get to neighbouring countries by road but have little chance of getting on a commercial flight without a passport. I don't recommend doing this because it is likely breaking the law.
Given they were previously named on their mother's Pakistani passport this might mean they have a better chance of getting a Pakistan passport of their own more easily than getting an Indian one.


Exactly what is "low heat" for making cheese sauce?

Question: Having a poor track record of making cheese sauces, I'm determined to do it right at least once in this decade.   I read that one should use "low heat" only.  Too much heat causes the cheese to go stringy or clumpy.  Okay - but just what is "low heat"?  Warm but not beyond what I can stick my finger in comfortably?  Can someone put a number on it, degrees centigrade?
Answer: Cheese have enzymes. Enzymes break quickly and easily at 150F/65 C. 50 Celsius for a short period of time should suffice to melt you cheese without breaking the protein structures.
I have committed the same mistake many times. Actually the fist day my in laws where over i tried to impress them with homemade pasta and cheese sauce. My Cheese sauce clumped.   My back up plan is to add milk tomato sauce put it on the blender until it liquifies.
Comment: @Darenw Your question triggered my curiosity because different cheeses behave very differently. My question was mostly based in experience and my understanding of enzymes. And since you're asking for the temperature I thought to myself certain cheeses will have different temperatures depending on its water content. I found this forum thread where someone actually tested. http://cheeseforum.org/forum/index.php?topic=3128.0 and some tips http://www.finecooking.com/articles/how-to-melt-cheese.aspx
Answer: In a cooking instruction, "low heat" doesn't refer to the temperature the sauce reaches, but the speed at which you heat it up. Many stove rings (hobs) are marked min-2-3-4-med-6-7-8-max. On that scale, a low heat would be 2 or 3. Very low heat would be min or 2. Left on the stove long enough, even at min, your sauce will boil. The key about using low heat is that it probably won't boil in the amount of time you need to melt the cheese, and that's good.
I make cheese sauce regularly (did so tonight) and I start at med to melt the butter, turn it down while the roux cooks, add milk, once it's pretty thick I turn it down even further, or just turn it off since an electric element will hold heat for a while, then stir in the cheese. If it ever happened that my cheese wasn't melting I guess I would turn the heat back up a bit, but that hasn't happened to me.


What happens with a CD-KEY of a steam game if I add the same game through a pack?

Question: I have a game added to my steam library a long time ago (I redeemed it with a physical retail CD-key, let's call "XXXX") and then I would know what happens with this retail cd-key if I buy a steam key ("YYYY") of a pack collection of various games that includes this same game that I had redeem with a retail CD-Key, so then after activating this pack will I have the same retail CD-Key still for this specific game (the "XXXX"), or it will be changed for other different key ("ZZZZ")?
Comment: Are you buying the pack through Steam itself or a service such as Humble Bundle? Or is it a physical CD for a bundle?
Comment: And you're asking whether or not you'll be given the exact same key you used for a game, correct?
Comment: A steam key of a pack bought of others store differents of steam (for example humble, amazon, gmg), I know that the games that I owned in my library won't be added/duplicated nor give me extra copies, but I have the doubt of if the retail cd-keys of these owned games will change for new keys or remain with the same original retail cd-key.
Comment: As far as I know: once redeemed: forever locked to that account. Retail or not doesn't matter. You can't sell that retail game anyway. because that key is locked to your account.
Answer: As you know, CD keys can only be used once (or deactivated before it is used, from the developer's side). Once used, they'll go into a list of used keys, where it'll be eventually (after a very long time^) be reused.
If you apply a new CD key containing a subset of games and you own copies of one (or more) of the games you have already owned is in that bundle, you do not get a second copy, or a new CD key in replacement to the old one.
All you get is the remaining games (and DLC's) in the bundle that you do not already own that the key grants.
However, there are exceptions to the rule but only apply to games purchased from the Steam Store, and are granted as a Steam Gift (item).
^Open to speculation
Comment: "where it'll be eventually (after a very long time^) be reused." Source?
Comment: "Open to speculation"


How to root Lenovo A319?

Question: I have a Lenovo A319 and Kingo Root didn't work on it. I badly need to root my phone because it has collected lots of bloatware. Please help.
Comment: @Manubhargav just saying, but LMGTFY is considered rude. A better solution is to provide the key word, and at least 1 direct related-link (e.g. XDA forum)
Comment: @AndrewT. Oh, I posted that as a fun way of saying google it. But thanks for letting me know about it
Answer:
Try "Root Genius for PC" to root your phone.
Download it from here Root Genius for PC
Install it on your PC, Run the Software.
Connect your Phone with PC using USB Debugging.
When your Phone get connected-> You will see in the Software, there is root button, Click on that, wait for 15-20 minutes.
After sometime, your phone get rooted, and you can see "Kinguser" app is been installed.

How to root Lenovo A319?


Is there a recommended party size for Waterdeep: Dragon Heist?

Question: I'm planning on starting a campaign of Waterdeep: Dragon Heist tomorrow, but it's looking like we may only have two players (plus me as DM) for it. The other published adventures I've used (Lost Mine of Phandelver and Storm King's Thunder) each say a recommended party size for them, which we haven't always had but helped me figure out how much I needed to adjust the included encounters when we had fewer players. But I can't find within Dragon Heist the party size that it's designed for. Due to it being more of an intrigue-based campaign than a hack-and-slash style, does it work just as well if you have two PCs or six?
Answer: While not stated explicitly, the norm still appears to be 5 players. However there are useful suggestions on the internet for balancing the module for different numbers of players. One such example is by a reddit poster who seems to have prepared explicit adjustments for various encounters.
With two players, you can also consider letting each player run a second character or a sidekick.
Comment: DDAL08 seems to be approximately the same - 5 players is considered Average, whereas 6+ is considered Strong and 3-4 is considered Weak.


Are donations to public schools tax deductible like a 501(c)(3) organization?

Question: In the United States,  are donations to public schools like a local elementary school deductible in the same way that donations to a  501(c)(3) charity or a church are deductible?
Comment: @Vitalik Thanks for fixing the 501(c)(3) reference.
Comment: @littleadv me? CPA? no, never was, never will be. My guess was wrong so i am deleting my comment.
Answer: See IRS Pub 526:

Deductible As Charitable Contributions
Money or property you give to:
[...]

Nonprofit schools and hospitals
Federal, state, and local governments, if your contribution is solely for public purposes (for example, a gift to reduce the public debt or maintain a public park)

Your local school is likely nonprofit and a branch of the local government. If so, yes, the donation is tax-deductible.
See also IRS Pub 17, which has some duplication from Pub 526:

Organizations That Qualify To Receive Deductible Contributions
[...]
You can ask any organization whether it is a qualified organization, and most will be able to tell you.
[...]

Most nonprofit educational organizations, including the Boy (and Girl) Scouts of America, colleges, museums, and daycare centers if substantially all the child care provided is to enable individuals (the parents) to be gainfully employed and the services are available to the general public. However, if your contribution is a substitute for tuition or other enrollment fee, it is not deductible as a charitable contribution, as explained later under Contributions You Cannot Deduct.
Comment: @duff - Right. I think our local PTA either has or is pursuing 501c3 status.
Comment: Also note, that organizations associated with the school may or may not be tax-deductible. For example, sports boosters, or a club.
Answer: Donations to most public schools are tax deductible if it's used for public purposes; public charter schools might be an exception so I would pay attention to that. Also as mentioned above you want to make sure you are donating to the public school/government unit and not some "affiliated" organization like a booster, pto, pta, etc. which requires 501c3 tax exemption. (actually I think schools aren't considered individual entities and are part of the district - districts and schools should be clearer about how to make payment)
US Code 170
There shall be allowed as a deduction any charitable contribution (as defined in subsection (c)) payment of which is made within the taxable year.
...
(c) Charitable contribution defined
For purposes of this section, the term "charitable contribution" means a contribution or gift to or for the use of—
(1) A State, a possession of the United States, or any political subdivision of any of the foregoing, or the United States or the District of Columbia, but only if the contribution or gift is made for exclusively public purposes.


How do I prevent furniture from leaving dents in the carpet?

Question: Furniture tends to leave dents in carpet when left for any length of time. Specifically, my chair tends to leave imprints where I have it in my room. How would I go about preventing this?
Comment: Are you asking about dents(compression) or stains(discoloration)? Or both?
Comment: @ErinGoBragh dents.
Comment: Also see the following question for suggestions on removing dents (not preventing them).  http://lifehacks.stackexchange.com/questions/5763/how-to-get-rid-of-carpet-indents
Answer: Furniture coasters work well. You can also make a furniture coaster from scrap carpet by cutting them into squares (or whatever shape makes you happy). Place the coaster between the leg/foot of the furniture and the carpet. It will not prevent the dents, but will reduce them as the weight of the furniture is spread across the coaster.
Comment: I'm iffy, I really doubt coasters help with the denting, I think they are more helpful when it comes to sliding furniture or scratching wooden floors
Comment: When I moved into a new home last year, I had this problem and I did this for the legs of a table. I cut them a little wider than the width of the leg to spread out the mass. I've come across some of the spiked coasters on Amazon which seem like they'd do the trick.
http://www.amazon.co.uk/Medipaq-CARPET-SAVERS-Furniture-spikes/dp/B002EWOGN4
Answer: Furniture coasters with several push-pins jammed into them might do the trick.

Since the push pins stick out of the bottom of the furniture coaster, they will be what touches the floor, not the coaster. Since they are narrow, they will most likely slide between the upright threads of the "pile" of your carpet, so none (or very few) of those threads should be bent. And since there are multiple thumbtacks, the weight of the furniture and anybody sitting in it will be somewhat well distributed (as opposed to just using a single thumbtack to raise the furniture).
You'll need to get pretty strong thumbtacks for this; plastic thumbtack heads may break. I'd imagine that metal or wood would be best. The heads should be as tall or almost as tall, as the length of your carpet's pile.
Comment: Hm, Interesting. Have you seen or read anything that says this will work? When you sprawl out across a couch at the end of a long day, not only are there vertical forces, but pretty substantial *horizontal* forces trying to push the couch across the floor. I suspect a tack-in-a-coaster will be wrenched free pretty easily in that scenario, and you'll end up with either broken tacks or (more likely) the tacks splayed out across the floor.
Comment: Or, you can buy "spiked" furniture coasters with the nubs already in them, like [these](http://www.floor-protection-resources.com/prodimages/Slipstick-Square-Carpet-Castor-Cups-Clear-300.jpg) or [these](http://ecx.images-amazon.com/images/I/71Od71zX8WL._SX522_.jpg).
Comment: @RobertCartaino Good point. This was just off the top of my head. Tacks are the first thing I could think of that had the basic form I was looking for, but they may not be sturdy enough. (And J.R. pointed out that there are spiked furniture coasters which have certainly addressed the shear forces!)
Comment: @J.R. Cool! So someone else though of this solution already. Makes sense.
Answer: Fold a piece of paper 6 times. Make sure that the area of paper after folding 6 times is greater than c/s area of the leg. See that there are no edge point directly facing into the carpet and then put that paper below the leg. This hack should do the job temporarily.


What is "the OP"?

Question: I've heard "OP" used on several SE sites. I think it refers to the person asking the question. Is that right? Where do those abbreviations come from? Is there a specific FAQ type page that contains a list of these abbreviations?
Answer: http://en.wikipedia.org/wiki/Internet_forum#Thread

A thread (sometimes called a topic) is a collection of posts, usually displayed from oldest to latest, although this is typically configurable: options for newest to oldest and for a threaded view (a tree-like view applying logical reply structure before chronological order) can be available. A thread is defined by a title, an additional description that may summarize the intended discussion, and an opening or original post (common abbreviation OP, which can also mean original poster) which opens whatever dialogue or makes whatever announcement the poster wished. A thread can contain any number of posts, including multiple posts from the same members, even if they are one after the other.
Comment: Just for comparison, I've been using OP to mean Original Poster since around 1995 and I never noticed anyone use it to mean Original Post, specifically, but in many cases it works either way, so I wouldn't know if I interpreted it differently from the author.
Comment: So...are there other abbreviations?
Comment: Per the quote, OP carries a contextually-driven meaning. It can mean the Original Post (most common, IMO), and Original Poster, referencing the user specifically. I can't think of any other abbreviations at this moments, but there are many more relational terms, such as;

The parent (the commenter/poster one level above), grand-parent (two levels above), and occasionally but not-often, sister/brother/sibling. Note that most of these relationship terms are only used on sites that have threaded comments such as Slashdot, Reddit, and some blog systems. Not so much SE.
Comment: A somewhat less common but perhaps more clear term would be TC, for thread/topic creator. It removes the ambiguity of referring to the post or poster, but at least as far as SE is concerned, OP seems to be the more widely used term.
Answer: OP = Original Poster (or sometimes Original Post).
There's a good FAQ here.
Comment: Although not a down voter, it is hard to see how this answer adds much value to the accepted answer.  Cheers
Comment: I wonder what's with the down votes? The answer is short and to the point.
Comment: The OP asked for an FAQ.

What is "the OP"?


Bike patch glue help

Question: So I popped my tire manualing down a curb and I went to patch it but I didn't seem to have any glue left in my old tube of glue, so I went to the bike store and bought a new thing patch kit(cheaper to buy a new kit then a thing of glue) and I get home and go back to fixing my tire, I used the cap of the glue to pierce the top, I then tried to squeeze some glue out and heard a popping sound, I squeezed some more and there wasn't any glue in the brand new tube of glue I had just bought and opened. Did the bike store rip me off? Or did I do something wrong?
Comment: The store didn't make the patch kit, so they didn't rip you off. Manufacturing errors happen. Check there really isn't any glue (or substantially less glue than there should be) and take the kit back to the store and ask for a replacement.
Comment: Could have been old stock where air had got through the seal and set all the vucanising fluid.
Comment: It's not uncommon for there to be a large bubble of air in there, but, if you place the tube on a flat surface and press it flat, starting from the "tail" you should be able to get a reasonable amount of glue out.  If not, return it to the store for replacement.
Answer: If you buy something from a shop and it doesn't work, take it back and explain what happened. They'll almost certainly offer you a refund or a replacement.
Answer: I've had this happen with very old glue. I think the shop will understand the issue and replace it.
Answer: You can get small tubes of glue the same size as is in a patch kit. Some stores sell them, some don't, but they should be cheaper than a whole patch kit. They're also available mail order -- you can get a whole pile of them cheap. You can also get a larger can as well. The small tubes are nice tho because, when opened, the glue dries up quickly. This can happen even when they're unopened, as you found out. The glue in the kit you bought likely had a defective tube and it dried up while sitting on the shelf. Hopefully the shop replaced it.

Bike patch glue help


What is the purpose of "A-DEP" mode on Canon cameras?

Question: What is the purpose of the "A-DEP" shooting mode on Canon cameras, for example the T3i/600D? In what kind of situations is it helpful - for example, under low light conditions, higher ISO or when using a lower shutter speed?
Comment: I guess, adding to Philip's answer, is that the purpose is to overcome the lack of a dof scale printed on the lens with moving cursor at focal position.  What you ought to use is the DOF Preview button, which is near the lens mount towards the bottom of the body (that used to be a lever that worked the lens mechanism, thus the characteristic placement).  Or zoom in on a review of a test shot.
Answer: The purpose of A-DEP is explained in the manual (page 101):

Objects in the foreground and background will be in focus automatically. All the AF points will function to detect the subject, and the aperture required to attain the necessary depth of field will be set automatically.

Or in other words, it's useful when you don't know what aperture to set in order to get everything in focus - it lets the camera analyze the scene, pick out the "interesting" objects and then choose the right depth of field.
That's the theory anyway. In my experience, what it tends to do is analyze the scene, pick the wrong objects and give me a photo with a wonderfully sharp tree, only slightly ruined by the blurry person standing in front of it, so I'll tend to avoid A-DEP mode along with anything else where the camera chooses the active focus points.


Is there a way to automatically backup skype chat in the gmail account for Macs?

Question: I would like my skype chat history to be searchable through my gmail account, hence my question is if there are any apps similar to www.g-recorder.com that would work on OSX?
Answer: I'm interested in this as well and G-Recorder answered me through email that they are on the way to Mac version.
Answer: G-Recorder released MAC version. Please note that Skype API has a problem on MAC Lion that we cannot workaround. So our team and lots of our MAC users wait for fix from Skype team.
And yeah, you already noted, I'm one of G-Recorder developers.
[EDIT]: Skype released beta that fixes Lion problem