Guru Purnima celebration

Question: Hindus and Buddhists celebrate Guru Purnima every year. What is the significance of celebrating Guru Purnima? Are there any specific rituals that are expected to be done during the day? Also, when does it occur?
Comment: The true meaning of Guru is "one who dispels darkness of ignorance". "Gu" means "darkness of ignorance" and "Ru" means "one who removes". Guru resembles the trinity Brahma, Vishnu and Shiva. Brahma is creator. Guru creates or inculcates knowledge in the minds of the students. Guru is Vishnu. Lord Vishnu maintains the creation. Similarly Guru helps in keeping up the knowledge. Guru is like Shiva. Shiva is the destroyer, who destroys and creates anew..
This link is very useful, especially for students/scholars:- https://www.youtube.com/watch?v=944Fik5Y66Y
Answer:
अखण्डमण्डलाकारं व्याप्तं येन चराचरम् ।
तत्पदं दर्शितं येन तस्मै श्रीगुरवे नमः ॥
Akhanndda-Mannddala-Akaaram Vyaaptam Yena Cara-Acaram | Tat-Padam
Darshitam Yena Tasmai Shrii-Gurave Namah ||
Meaning: Salutations to the Guru ,Whose Form is an Indivisible
Whole of Presence, and By Whom is Pervaded the Moving and
the Non-MovingBeings,  By Whom is Revealed  that Feet , Salutations to
that Guru.  See More

The festival of Guru Purnima, (गुरु पौर्णिमा) is dedicated to shree Ved Vyasa and also known as Vyasa Purnima (व्यास पौर्णिमा) is celebrated on the full moon day of Hindu Month Ashad (आषाढ़) . The River Beas (बियास)  is  named after Ved Vyasa. He practiced penance on its banks and compiled the four Vedas, the Mahabharat and the Eighteen Purana there. Vyasa is considered by Hindus as Chiranjivi (चिरंजीवी) or immortal, one who is still living and walking the earth for the well-being of all.
Vyasa Purnima or Guru Purnima is a day of great significance in Hinduism. Guru Purnima or Vyasa Purnima is a  symbol of the Guru-shishya tradition.
Guru or teachers play key role in one's life. Spiritual gurus nurtures and modifies our lives. They make us understand the difference between right and wrong and good and evil.
On this day, all  devotees,  disciples , Students  worship Shree Ved Vyasa in honor of his divine personage and all Hindu's perform a 'puja' of their respective "Guru's  or Gurudevs" (गुरुदेव). By touching the feet of Guru's , they receive their well whishes.
Read more about Guru Purnima
Answer: To excel in any field a learnt & experienced person is required and the one who teaches & guides you may be termed as guru where as the one who is self realized and can set you from cycle of life and death is spiritual guru or sadguru. Guru can appear to be an ordinary individual to all. He can be understood and experienced only by His blessings. He is neutral, He don't want any worldly things, He is self sufficient. He has become equal to bramha, the oneness. So the disciples worship and render dedicated service to his Guru to gain knowledge and liberation! Guru has infinite forms, Guru takes many bodies and descend to earth and by each form He preaches a specific (bhakthi/karma/gnana/..) to each of His follower.
Guru purnima is Guru worship day. One has to remember the Guru parampara/lineage from parabramha to His Guru. Guru pada puja or paduka puja (worshiping Guru's holy feet. If Guru is far or has left His body, His footware is worshiped) is done. It falls on the day of full moon, Purnima, in the month of Ashadh (June–July) of the Shaka Samvat, Indian national calendar and Hindu calendar.
Answer: To answer the first question:

Guru Purnima is called the day of the Master but it is actually the
  day of the Devotee. Guru Purnima is New Year for spiritual seeker.
  There are three types of people who come to the Master, the student,
  the disciple and the devotee.
A student goes to a teacher and learns something, gets some
  information and then he walks out of the School. There is no more
  information, just like looking at a guidebook, like a tourist guide.
  You go with the tourist guide to see a place, and the guide shows all
  the places, or like a Traffic Police, sometimes he directs you or like
  you ask someone, "Where is what?" and they'll give you some
  information. You take it and you say, "Well, thank you" and there it
  is finished, isn't it? You went to primary school, middle school, and
  whatever grade you call it, you collected information; you learned
  about mind, you learned about computers, learned about mathematics,
  and learned how 2+1 is 3. The student is one, who collects
  information, but the information is not knowledge, it is not wisdom,
  is it not so?
Then there is the disciple, the disciple follows the example of the
  Master. But a disciple is with the Master for the sake of learning
  wisdom, for the sake of improving his life, for the sake of attaining
  enlightenment. He has a purpose, a cause, so he is not just collecting
  information, but he goes a little deeper. He is trying to bring a
  transformation in his life. He wants to make sense out of his life.
  That is a disciple.
And then there is devotee. A devotee is not there even for wisdom. He
  is simply rejoicing in love. He has fallen in deep love with the
  Master, with the Infinity, with the God. He doesn't care as to whether
  he gets enlightened or not. He doesn't care as to whether he acquires
  a lot of knowledge or wisdom or not. But that very moment, and every
  moment, he is immersed in divine love that is enough for him or her. A
  devotee is very rare to find.
Students are in abundance, disciples are a few, but the devotees are
  rare.
It is nothing great to become God or be God. Whether you want or not,
  all are already Gods. A stone is also a God. You are also a God.
  Everything is God, God is already there, but it is great to become a
  devotee. Do you see this? Everything, whether you want it or not, is
  already God, but the love, devotion, has flowered somewhere. Where the
  devotion has flowered totally, the flower has blossomed, that is a
  devotee. Attraction is everywhere, love is somewhere, but devotion is
  again rare. Devotion is very beautiful. A student comes to a Master,
  Teacher, and Guru with tears in his eyes. There are so many problems,
  and when he leaves, he is carrying the same tears, but the quality of
  the tears is different, it is of gratitude. Still tears flow, but
  those are of gratitude, of love; it is so beautiful to cry in love.
One, who has cried even once in love, knows the taste of it, of
  surrender and of devotion and the entire creation rejoices it. The
  entire creation is longing for only one thing, the transformed tears,
  from salty tears to sweet tears.
One of Buddha's disciples named Sariputra got enlightened. When he got
  enlightened, Buddha told him, "Now you go ahead, go into the world and
  preach, teach and do the same work I do, carry on my work." Now
  Sariputra left Buddha, but he was crying and crying and people asked
  him, "Why are you crying when you are enlightened?" He said, "Who
  cares about this enlightenment, it could have waited, I would have
  waited. I didn't even bother about it or asked for it because the joy
  of being at the feet of Buddha was so great. Being a devotee was so
  great, now I am missing this, I would have preferred that to this
  enlightenment."
There is no separation, there is no difference, there is no distance,
  yet it has a different flavor, different joy. That is a devotee, a
  devotee can never fall, he cannot fall, and there is no chance for it.
When Krishna was leaving his body, he spoke to Uddhava. With tears in
  his eyes, "I can't stand the amount of devotion these Gopies have for
  me, go and tell them, these devotees of mine that only they can free
  me of their gratitude and of their love." It is so beautiful, he
  rejoices, "Go, tell them that is the glory of devotees, I am not in
  heaven, I am not in temple, but where my devotees sing, I am right
  there". Devotion is something that can move even the rocks.
There once was a Zen Master who always thought that he was
  enlightened. He went around saying, "I am enlightened". He happened to
  meet one of his Masters who gave him a puzzle, called 'koan'. The
  'koan' was "the statue has eyes, the tears roll down silently".
  Hearing this Zen Master was shaken and he said, "There is some depth
  in it".
Love is something that even the Divine rejoices in it. The infinity
  longs for you as much as you long for it. It is waiting to receive
  you. God is as anxious as you are to be near. So when a devotee
  flowers on this planet, God is very happy. That is why Guru Purnima is
  the day of the Devotee.
Like fatherhood and motherhood, there is Guru-hood. We all have to
  play Guru-hood at least to somebody. We do play! Consciously or
  unconsciously you are all Guru to somebody. You keep giving advices
  and guiding people, giving them loving care! You all do this, but do
  it 100%, without expecting anything in return: that is living the Guru
  principle. There is no difference between the divine, the Self and the
  Guru. They are all one. Meditation is relaxing and reposing. Think of
  all the things to be grateful for and ask what you want for the future
  and bless everyone. We receive so many blessings and we should also
  bless all those who are in need.

From an article by Sri Sri Ravi Shankar: http://www.artofliving.org/wisdom/knowledge-sheets/guru-poornima

Guru Purnima celebration


Use of Roman numeral notation when a new key is introduced within original key

Question: I would like to use Roman numeral notation for songs and do not know what to do when the piece transitions to a new key: e.g., from C to E flat major.  I know this is basic, but do I try to use the numerals for the original key, or the new key?  The transition is all within the original key.  An example song:  "We'll Be Together Again", in C major.  How do you notate the transition chords to E flat?
Comment: The proper term for new key would be the key you modulate to. DO you want me to edit better terminology in?
Comment: It's a modulation, rather than a change of key.
Answer: You would have to indicate the change of key by using the letter names of the key you are going to and you also indicate whether the key is Major by the use of a capital letter and minor through the use of lower case letters.
So you can for instance have the following. (assuming we have to do with Major keys here.)
C: I IV V Eb: vi ii V
Answer: You start using the roman numerals for the chords in C major, like I,V,VI,VI etc and let's say that the C major chord chromatically changes to C minor (the vi of Eb major), you could write vi/Eb major and continue writing the roman numerals on Eb.
For the first 4 chords in the second line here:

You could use the roman numerals:
ii/Ab major, V, I,IV.
Answer: If you are staying in the same key then bIII will be Eb major biii Eb minor. A Neapolitan 6th in C major would be Db/F bIIa I believe. I am sorry about the b representing both flats and second inversion chords here.


How to escape from an aircraft if the door is not armed?

Question: Following the question about arming the door, the link states that doors are usually armed before engine start. What if something goes wrong when passengers are already boading with doors un-armed how to escape from the airplane?
Answer: The door the passengers are loading through is obviously one route, back down the jetway or stairs.
The door being "armed" does not affect whether it can be opened or not.  When the door is armed, opening it will also automatically inflate the escape slide.  When the door is disarmed, the slide will not inflate.
Additionally, each door has a manual inflation handle for the escape slide which the crew can use to deploy the slide if needed.
I could not find a non-copyrighted picture to include.
Comment: It's fine to use a copyrighted image for educational purposes. It's called "fair use".
Comment: Not every picture though, even fair-use has limitations. But thats a discussion for the META site  @ColeJohnson
Comment: Cockpits also have escape ropes.
Answer: If the passengers are boarding, the stairway or jetway will still be in place, so this would still be the main route to evacuate the aircraft. There is no requirement for the door to be armed and for the slides to be triggered during an evacuation while the aircraft is still "docked".
If there is an emergency onboard after the stairway or jetway has been removed, but the door not having been armed yet, the evacuation slides can be trigged manually if they are needed.


How to create custom preview for content type in Drupal 7?

Question: I am implementing a content type called "Product" which has some 8 to 10 fields.
While creating new product details under that content type "Product" client wants the custom preview of the content.
The default preview while adding content is really weird and it does not look good.
I have searched a lot on google but there is no any contributed module available for it.
So please tell the way other than custom module to implement it ?
Answer: Something like Page Preview may help you.


Is there a mitzvah to escort a non-Jew?

Question: There is a mitzvah to escort a traveler along their way. Does this mitzvah apply to escorting a non-Jewish traveler or guest as well?
Answer:
"Avraham walked with them to escort them" - B'reishit 18:16
"It is a positive commandment of Rabbinic origin to visit the sick,
  comfort mourners, to prepare for a funeral, prepare a bride, accompany
  guests, attend to all the needs of a burial, carry a corpse on one
  shoulders, walk before the bier, mourn, dig a grave, and bury the
  dead, and also to bring joy to a bride and groom and help them in all
  their needs. These are deeds of kindness that one carries out with his
  person that have no limit.
Although all these mitzvot are of Rabbinic origin, they are included
  in the Scriptural commandment Leviticus 19:18: "Love your neighbor as
  yourself." That charge implies that whatever you would like other
  people to do for you, you should do for your comrade in the Torah and
  mitzvot." - Hilchot Aveil 14 (the rest of the chapter is worth reading
  as well)

Considering the people Avraham were escorting were by logic not bnei Yisrael, then yes, you should escort anyone(it seems even the stam goy). If they eat at your table and they say "thank you", tell them to please "thank God".
If you can, if they're not shomer sheva mitzvot bnei Noach, you should try to even pray for them similar to Avraham praying for the people of Sodom, Avimelech, etc.
Comment: It's the Rambam's logic post-mt-sinai.

" Accompanying them is greater than showing them hospitality. Our Sages said: "Whoever does not accompany them is considered as if he shed blood." "

Rambam says even for non-Jews as not to cause social issues.
Comment: Kidush-hashaem?
By the way, I did that once to a couple and they told me "God bless you". I'm pretty sure they were christian, would that be a problem of "ושם אלהים אחרים לא תזכירו לא ישמע על פיך" ?
Comment: A friend of mine was brought up Modern Orthodox but has drifted Yeshivishe due to his children. Once I asked him why does he always walk out of the office with the people he is interacting with---most of whom are not Jewish. His response was that he was attempting to emulate the prophet Abraham who did the same. This, of course, does not source the origin of such behavior, but it does seem to confirm that some Jews are convinced "escorting" people, Jew or Gentile, on their way, is important.
Comment: I don't find your logic convincing in the slightest. Pre-mt-sinai is a different ballgame

Is there a mitzvah to escort a non-Jew?


Tablets Apps have narrow popups . Is it a problem?

Question: I noticed that a lot of tablet applications including Amazon, Overstock, Wayfair and many others are using too narrow popups that are sitting in a very inconvenient zone and hard to reach with thumbs. Is it a real problem or it's so minor that UX/UI designers should not even worry about it?
Comment: Each of those examples includes a text-field, so the user is going to have to type, meaning that their hands will be in a different position.
Comment: Users don't have to change hands position for typing. Most likely they will use thumbs but in order to set focus into the input field they have to stretch their thumbs or change hands position which is very inconvenient. And that's my point. I really don't understand why the popups are so narrow and inconvenient to reach. And I see these narrow popups in every second application.
Comment: Developers are lazy, and iOS UIKit centres popups. This is not the result of design, it's the result of minimum effort development based on the framework's defaults. You are right to consider the users. There is nothing wrong with being concerned about this problem, and nothing wrong with thinking about making an adaptable and user customisable solution. But... best of luck finding developers who will do it for you. Most apps are rushed out the door as soon as possible, with the least possible consideration of the user because there are other matters more pressing to the company and devs.
Comment: Almost the entire field of UX is a hoax and a ruse started by folks bad at development and poor at design, lacking in creativity and with a complete absence of empathy... yet wanting a pathway into the world of app and web hype.
Comment: Anyone actually taking the field seriously will say something like "interaction design". Most people riffing on user experience are looking backwards for stats in support stats for believing in stats.
Comment: @Confused "Most people riffing on user experience are looking backwards for stats in support stats for believing in stats" got any stats on that? ;)
Comment: Epic. 9 more characters to go....
Answer: It is a problem if users say it is a problem, and if these big companies haven't done something about it then I'd say that it isn't affecting their sales/transaction completion (although it is difficult to measure the impact directly). I will illustrate some points that may help you to decide how much of an issue this might be.

I don't know if this is exactly how someone holds a tablet when they are in the context of making purchases online, but it looks like even the way the person is holding the tablet isn't that comfortable. From my experience if someone is using the tablet for a decent amount of time the device is probably going to be lying flat or propped up on an angle. In these types of configurations the user will have at least a free hand to make contact with the centre of the screen.
The problem with designing for tablet is that even with a responsive design framework you tend to want a fixed size for modal windows because the content usually won't vary due to viewport size differences (other than the size of the font or image). So what you see as being a poor user experience is possibly the designers trying to cater for fixed content being displayed on various screen resolutions and sizes and is a compromise rather than by choice.
It is not normally convention to align things to the left or right hand side of the screen unless it is a fixed element (e.g. navigation menus, search bars), and popups can occur potentially anywhere. Positioning things on either side of the screen would also assume a 'handedness' in how users interact with on-screen elements (disregarding whether there is left or right hand biases), so by default it should sit in the middle of the screen.


How to access a parent paragraph twig file from a child node twig file?

Question: In my bootstrap theme, I am trying to make the id of the paragraph the same as an attribute for each of the child nodes, so an accordion will work properly. I have tried looking at doing it through hooks, but I can't seem to access the paragraph data from my node hook.
Answer: You can use hook_preprocess_paragraph hook to set the same id to all child nodes, in the below code snippet example all child nodes will have paragraph-PARAGRAPH-ID as id.
use Drupal\Component\Utility\Html;
/**
 * Implements hook_preprocess_HOOK().
 */
function myModule_preprocess_paragraph(&$variables) {
  $paragraph = $variables['paragraph'];
  $identifier = Html::cleanCssIdentifier('paragraph-' . $paragraph->id());
  $variables['attributes']['id'] = $identifier;
}

Comment: How would I put the paragraph id in a different attribute like "data-parent"  in the child node?
Comment: try with `$variables['attributes']['data-parent'] = $identifier;`  instead of `$variables['attributes']['id'] = $identifier;` .
Comment: I know I can do something like $variables['var_name'] to have it be a variable in the paragraph twig file. How would I do this to get the variable (in my case paragraph id) inside the children node twig files too?


What happens if your opponents never let you win the bid?

Question: In other words, they out bid you even if they have a very bad hand just to prevent you from getting any points above the line?
Comment: I think you mean *below* the line - that's where points for successful bids go, while penalties and other bonuses go above the line.
Answer: I will expand on Benjamin Cosman's answer by noting that:

The behaviour you are observing is bad bridge; and
The (scoring) line in Rubber Bridge is simply that, and a means (other than a time limit) for ending the match. The winner is determined by the total of points obtained both below and above the line.

However, to expand on point 1 above, learn to double the opponents to truly penalize them for their unsocial behaviour, and enhance your defensive skills to get those extra tricks that turn a collected penalty of 100 or 200 into 800 or even 1100. A couple of those should slow down your opponents penchant for stink bidding.
If collecting penalties is still insufficient, offer to play for a little pocket change. A one cent a point stake over 3 or 4 hours can comfortably net $40 to $80 profit over weak players. There are two common forms of scoring in money bridge: rubber and four-deal or Chicago. Tough money players will deliberately play rubber against weak players as it creates additional strategic considerations that those players fail to grasp. Only against players that they respect do they opt for Chicago scoring, as it reduces the luck element.
Finally, I will note that the scoring of doubled not vulnerable under-tricks was changed about 20 years ago. Formerly all doubled undertricks after the first were scored at 200 points each, but long experience revealed that this was inadequate. A change was made that the 4th and subsequent doubled undertricks not vulnerable undertricks  now became 300 points each, the same as when vulnerable. Make sure that you are using the current scoring table - and practice your doubling and card-reading skills.
Good luck!
Answer: I fear the other answers might be overthinking this. If your opponents outbid you and you believe you can set them several tricks you double them. This is the element in bridge scoring that increases the penalty your opponents pay for going set in their contract, and it serves as a disincentive for overbidding or over-ambitious "sacrifices" against opposing contracts.
If you find that your opponents don't care about the score penalties they incur when you double them and set them several tricks then you should move on to Benjamin's and "Forget"'s answers.
Comment: I would amend this to something like "*... and you believe you can set them at least two tricks, then you double them.*" This guidance provides one insurance trick, and on balance is much more profitable than waiting for an expected *several trick set*. If your opponents **never** make a doubled contract - you are not doubling enough.
Answer: There are three cases:
1: You are playing at a tournament.
First of all, you're probably not. There are many ways of playing bridge with different scoring systems. For example, in "duplicate bridge", you are scored based on how well you do compared to other players who played the exact same hand - even if you get lucky cards and make a small slam, you lose if another partnership bid and played the same hand to a grand slam. As far as I can tell, the kind of bridge you are talking about - "rubber bridge" - is not often used at competitive levels, presumably because it has more luck than many other systems. (I don't have a source for this though; please correct me if I'm wrong!) However, if you do find yourself playing tournament-level rubber bridge, presumably your tournament has rules in place for ending interminable matches, whether they're caused by sketchy opponent tactics or just weird luck.
2: You are playing for fun, with reasonable opponents.
If you are unable to finish a match, the Laws of Rubber Bridge have you covered:

Law 80 – Incomplete Rubber
When, for any reason, a rubber is not finished, the
score is computed as follows: If only one game has been
completed, the winners of that game are credited with
300 points; if only one side has a partscore or partscores
in a game not completed, that side is credited with 100
points; the trick points and premium points of each side
are then added, and the side with the greater number of
points wins the difference between the two totals.

So just agree that the match has to end now, award a bonus if appropriate, and see who won.
3: You are playing for fun, with unreasonable opponents.
Seriously, why are you doing such a thing? Here's what the Laws have to say (emphasis added):

The Scope of the Laws
The Laws are designed to define correct procedure
and to provide an adequate remedy whenever a player accidentally, carelessly or inadvertently disturbs the
proper course of the game, or gains an unintentional
but nevertheless unfair advantage. An offending player should be ready to graciously accept any penalty set
forth in these Laws or any adjustment or decision of an
Arbiter.
These Laws do not deal with dishonorable practices
where ostracism is the ultimate remedy.
Comment: Stink bidding in the right situation is good strategy. OP however asks what if they *never* let you win a bid. Hence the 3 cases: 1) at a competitive level, I'm sure the scoring system will penalize them appropriately, 2) if they're reasonable (not likely, given the interminable stink bidding), they'll still admit you beat them at the end of the night, but 3) if they're unreasonable ("nyah nyah you haven't won the rubber yet and never will"), as far as I know the rules of rubber bridge do not have any way to force the game to end; so what would *you* do other than just not play with them?
Comment: I find your 3rd point excessive. The scoring tables (particularly since the modification some years back to non vulnerable doubled undertricks) are more than adequate to ensure that competent players can outscore a pair determined to just *stink bid*. Further, *stink bidding* is definitely ***not*** a dishonourable practice. The finest players excel at it, ***and*** in knowing just when to do so for a profit.
Comment: Who cares? Seriously. Just double and keep collecting your doubled undertrick penalties. There is no compulsion to ever **end** a rubber, except as a terminating event for a match fragment. The contest always ends after an approximate period of time or number of hands is reached.
Comment: One remedy: Run up your score with "ten" or so, doubled, defeated contracts, then let them win a "rubber" of two "back to back" games when you want to go home. See how the score sheet is at the end of the night.
Answer: If you have a good hand, you should be able to make a bid or collect an offsetting penalty. So if your opponents consistently overbid, just double them (consistently). If you double them and they "get away" with it (e.g. make a game or lose less than the value of your "lost" game) when you do, you are being outplayed. Unless your opponents are very lucky (e.g. all of their finesses and "drops" are successful).
If you and your partner have 25+ high card points and an eight card suit, that's enough to make ten tricks most of the time. If that suit is a major, then four of a major.
Lets say you can bid and make four hearts. To outbid you, your opponents need to bid four spades (or five of a minor). But if you can make four hearts because you have 25+ high card points, your opponents should be able to make only six tricks in four spades (assuming an eight card suit) with their 15 high card points (or less). That would be down four, or 800 points NOT vulnerable. That one defeat should cost about the same as a "rubber" (two games to zero) and more than a two games to one rubber.
Comment: I would amend the 2nd paragraph to something like: "*If you and your partner have 25+ high card points and an eight card suit, that's enough to bid for ten tricks with reasonable confidence of success*'. There is never a guarantee that well-bid contracts will make - that's half the fun of the game. Otherwise, a good answer complementary to the others.
Answer: While it is not against the rules to do this, if an opponent keeps doing this, you should call the tournament director. They are able to exclude this person or pair from the tournament because bridge players are expected to be courteous.
Edit: to be clearer, when I read the word "never" in the title, I'm inagining an opponent with a grudge against you who stops at nothing to keep you from playing. Having the worst possible score does not matter to them.
Comment: Nope. There is nothing irregular or unethical with being a consistent overbidder, or with being a poor player, so this advice is entirely incorrect.
Comment: If an opponent has a personal grudge against you and structurally keeps you from playing by overbidding contracts nobody would ever bid, you most certainly can call the director.
Comment: "When your opponent is making an error - don't disturb him." Why would I call the Director? I will just collect my tops, and smile.
Comment: Do you understand how the game is scored? Consider both partnerships being vulnerable. If opponents *stink bid* to prevent our game, so we can't score the 500 point Rubber Bonus, we collect the exact same value with a two trick set doubled. If they do it twice more, we have won the equivalent of three rubbers, 1500 points, and we are all still both vulnerable. *This is precisely how strong players fleece weak players, and why they play **Rubber** instead of [**Chicago**](https://www.acbl.org/learn_page/how-to-play-bridge/how-to-keep-score/chicago/) scoring against such players*."


Are 2nd Order Edge Detectors More Susceptible to Noise?

Question: I am reading about edge detection and I read that 2nd order detectors are more susceptible to noise. Is there a mathematical proof to this ?
Answer: Suppose that the noise is a random vector $X$ with normal zero-mean components of variance $\sigma_i$, mutually independent, then for the linear combination (the $g_i$ being for instance coefficients of a FIR filter):
$$ Y = \sum_i g_i X_i\,,$$
the variance of $Y$ will be:
$$ V(Y) =\sum_i g_i^2 \sigma_i^2\,, $$
which boils down to $$\|g\|_2^2 \sigma_2^2\,$$
for a classical stationnary Gaussian noise.
Now start from $g^1=[1,-1]$, and assume you built higher order derivative by self-convolution, for instance $$g^2=g^1 \ast g^1 = [1 ,-2 ,1],$$ $$g^3 = g^1 \ast g^1  \ast g^1 =[1,-3,3,1] ,$$ etc.
You easily get that the coefficients of $g^n$ are $$g^n_k=(-1)^k  \binom{n}{k}\,.$$
Hence $\|g^n\|_2^2 = \sum_k    \binom{n}{k} ^2 = \binom{2n}{n}$ (a famous identity). For $n=1$, the amplification is $2$, for $n=2$ it will be $6$, and $20$ for the third derivative.
So the noise amplification roughly grows with the derivative order (based on Stirling's formula) as
$$\frac{4^n}{\sqrt{\pi n}}\,.$$
So all in all, noise power tends to explode with derivatives.
This does not happen at order $0$, if you consider that traditional low-pass filters having positive coefficients have finite sum, often equal to $1$. Hence, for those  $\|g\|_2 \le \|g\|_1=1$. For instance, if one takes standard smoothing "discrete Gaussian" filters of order $m$ with coefficients
$$b^m_k=\frac{  \binom{m}{k}}{2^m}\,,$$
then their $\ell_2$ squared norm is:
$$\frac{\binom{2m}{m}}{4^m}$$
and one sees that the $4^m$ term cancels in the asymptotics, and you get that, when $m$ grows:
$$\|h^m\|_2^2 \approx\frac{1}{\sqrt{\pi m}}\,,$$
and thus tend to reduce the noise power.
Finally, this is not the whole story, since we have not talked about edges, which traditionally are wide-band, and especially hard to detect in high frequencies. A study in the Fourier domains may lead to others aspects, that exceed my time today, but is addressed in @Olli Niemitalo's answer.
Comment: @Olli Niemitalo I meant asymptotics on the $\infty$ side, as derivative order grow, based on Stirling's approximations. I should mention that
Comment: @Olli Niemitalo What a great question! I have added details, hoping I did not make mistakes. I never thought abot that before, I will reuse that in lectures :)
Answer: If you assume the Edge Detection is SNR driven operation, one could find a Mathematical justification for this.
First, the variance of Additive White Noise with Variance $ {\sigma}_{n}^{2} $ at the output of a Linear System given by $ g $ is $ {\sigma}_{n}^{2} {\left\| g \right\|}_{2}^{2} $.
Let's look on an Image filtered by a derivative approximating filter $ g = \left[ -1, 1 \right] $.
This increase the Noise Variance by a factor of 2.
For 2nd order the filter is $ {g}_{2} = g \ast g = \left[ 1, -2, 1 \right] $ hence the factor is 6 (It comes from the reason the second time we filter the noise is correlated).
Now, the question does the signal (Edge) is amplified by the same factor?
Moreover, on areas where there is no edge, the probability to detect noise as edge increases.
To see intuitively, just operate 1st order method on the gradient of the image and see how much False edges you have now.
Comment: @LaurentDuval, I meant the factor is 2 for this filter. Your general answer is right of course. I did a mistake on the 2nd. Will fix.
Comment: Hi thanks for the reply. So if I were tweak your example by using the central differencing operator [ -1 0 1] and the 2nd order derivative [ 1 -2 1]. Then if I convolve with the central differencing operator I would get f'(x) = f(x+1) - f(x-1) + n(x+1) + n(x-1). Convolving with the 2nd order derivative yields f''(x) = n(x+1) + 2n(x) + n(x-1) + f(....) ? Is that why the noise variance goes up a factor of 4 ? n(x) is the noise present.
Comment: @Drazick I am very bad at answering today, yet, if the filter is $g$, for a independent normal random noise, I would have said that the factor would be $\|g\|^2_2$, hence $2$ and $6$ for $[1, 0, -1]$ and  $[1 ,2 ,1]$. Where is my mistake?
Comment: Ah sorry yes I meant to write 6 for [1, 2, 1] since the center is 2 and hence the variance of 2n(x) would be 4.
Comment: @Olli Niemitalo Very good, diversity!
Answer: Let's assume that the signal has a white (flat) power spectrum $|X(\omega)|^2$ of unity power $P_0$:
$$|X(\omega)|^2 = c$$
$$P_0 = \int_{-\pi}^\pi |X(\omega)|^2 d\omega = 1$$
$$\Rightarrow c = \frac{1}{2\pi}$$
The Fourier transform of the "differentiation" filter $g = \left[1, -1\right]$ is:
$$G(\omega) = 1-e^{i\omega}$$
The signal power after filtering $n$ times will be:
$$P_n = \int_{-\pi}^\pi |X(\omega)|^2|G(\omega)|^{2n} d\omega = \int_{-\pi}^\pi \frac{1}{2\pi}\left|1-e^{i\omega}\right|^{2n} d\omega$$
$$= 2^{2n + 1}\frac{\left(\frac{1}{2}(2n + 1)\right)!}{n!\sqrt{\pi}(2n + 1)}$$
$$\Rightarrow P_0 = 1, P_1 = 2, P_2 = 6, P_3 = 20, P_4 = 70\tag{1}$$
This is for a flat power spectrum all the way to the Nyquist frequency ($\pi$). We won't see those large gains if the signal is low-pass with a band-limit below the Nyquist frequency, for example at half the Nyquist frequency:
$$P_n = \int_{-\pi/2}^{\pi/2} \frac{1}{\pi}\left|1-e^{i\omega}\right|^{2n} d\omega$$
$$\Rightarrow P_0 = 1, P_1 \approx 0.73, P_2 \approx 0.91, P_3 \approx 1.33, P_4 \approx 2.09$$
For the higher orders of differentiation, if there was any white noise in the data, it would follow (1) and blow up in comparison to a signal that is low-pass with the lower band-limit, giving a hopelessly low signal-to-noise ratio. The situation will be similar for any signal that doesn't utilize the spectrum all the way up to the Nyquist frequency.
True edges are not low-pass, however, but have a -6 dB / octave decaying spectrum. After the first differentiation, a normalized edge signal $[\dots, 1, 1, 1, 1, 0, 0, 0, \dots]$.looks like an impulse: $[\dots, 0, 0, 0, 1, 0, 0, 0, \dots]$. Based on (1), the second filtering multiplies the noise power by a factor of 3 while the edge signal becomes $[\dots, 0, 0, 0, 1, -1, 0, 0, \dots]$, doubling its sum of squares power and not affecting its peak value. We can conclude that in the presence of white noise, compared to the first order edge detector the second order edge detector suffers from a $10 \log_{10}\left(\frac{3}{2}\right) \text{ dB} \approx 1.76 \text{ dB}$ worse sum of squares and $10 \log_{10}\left(3\right) \text{ dB} \approx 4.77 \text{ dB}$ worse peak to sum of squares signal-to-noise ratio.


操{みさお} : too many translations to be true

Question: I am a bit confused regarding the translations of the word 操 in my 漢字 book (Kanji et Kana of Hadamitzky, Durmous and Mochizuki), as they give : chastity, purity, innocence, constancy, fidelity and honour! So I wanted to know which ones were closer to the actual usage of this word, as most of these translations have already well-known equivalents.
Answer: If you need to be strict in meaning, let's use those well-known equivalents :-)
Honestly speaking, I find it hard to explain how it is actually used, because it's rarely used. Everyone has heard this word, typically sung in enka and Japanese folk songs (for example see なみだの操). But the concept of 操 is almost never used in today's education, discussions, essays, and so on.
If I understand correctly, 操 is basically an old-fashioned word which is close to 貞操 (chastity). It does not necessarily mean being a 処女 (virgin), and 操 can probably be used with a married woman. I tend to associate 操 with a stereotype of strong-minded, determined woman who is faithful to her husband or master.
When I was writing this, Joan of Arc came up to my mind...although she's not even a Japanese!
Comment: Thank you very much naruto! Also, as chastity came first, I guess I can use this word it for this primary sense only, or I risk to be unclear.


Recent past which tense I should use?

Question:
You have been replaced by another person.

You were replaced by another person.

You are replaced by another person.

If something happens in recent past, which tense should I use?
What is the meaning of the above three sentences?
Answer: All of your sentences are grammatically correct. Which you use depends on context: why you are saying this.

1.You are replaced by Bob.
  2.You have been replaced by Bob.

Both of these are cast in the present tense (have, are) and address your current status. Either might be used to inform you, for the first time, of your new status, or if you already know that you are moving to a new position to inform you of your successor. They mean essentially the same thing. The version with the perfect construction (you have been replaced) would be the more natural in most circumstances; that with simple present (you are replaced) has a decidedly stiff and formal ring.

I regret to inform you that senior management have made their determination: you are replaced by Bob. Please clear your desk by noon and surrender your pass to Security.

However, the simple version is more natural if your informant is describing multiple changes:

Sally moves over to Sales, you replace her as section head, you are replaced by Bob, and we're authorizing a new hire to replace Bob. Congratulations!

The simple present may also be used with future or contingent rather than present reference:

Under the new scheme, you move up to section head; you are replaced by Bob.

The perfect construction cannot be used here.

3.You were replaced by Bob.

This version is cast in the past tense (were) and addresses a completed event. It would not ordinarily be used to inform you of something new; rather, it recalls the event in order to say something new about its context:

You were replaced by Bob because we were unhappy with your handling of the Adams account.
We needed to free you up for fulltime work on the Bergson account, so you were replaced by Bob on the Adams account.
Answer: The most common tense choices for talking about the recent past are present perfect and past simple. Your first two example sentences are in these tenses, while the third is simply wrong.

You have been replaced by another person

The tense here is present perfect, which is often used to talk about the very recent past. This is the most natural way to describe something that has just happened. This usage is also much more common in the UK than in the US.

You were replaced by another person

Here the tense is past simple. Past simple can be used to talk about the recent past, however the present perfect tense is often a better choice because the implicit timeline is more clear.

You are replaced by another person

This sentence is a mixed tense and would not be used by a native speaker. There are a number of ways to correct it, the simplest being to replace "are" with "were" to make the sentence past simple.

Recent past which tense I should use?


Direct3D (DirectX 9.0) Code Samples from codesampler

Question: I want to learn Direct3D from codesampler.
But this website can't open recently.
Is there anyone know how to download the sample code from this website, thanks in advance.
Comment: You can find Direct3D 9 tutorials here too: http://www.directxtutorial.com/LessonList.aspx?listid=9 looks like that site is either down or shut down
Comment: For other versions of Direct3D and more advanced tutorials: http://www.rastertek.com/tutindex.html
Answer: It looks like www.codesampler.com has lost their domain registry, and the Internet Archive Wayback Machine hasn't found that website since late 2016. It's probably just gone.
If you are looking to learn Direct3D today, you should focus on Direct3D 11. It's supported for Win32 classic desktop apps on Windows 7, Windows Vista SP2, Windows 8.x, and Windows 10. It's also supported on Xbox One and Universal Windows Platform apps. Direct3D 11 development is fully supported in modern versions of Visual Studio, and all the headers and the HLSL compiler you need are part of the Windows 8.x SDK and the Windows 10 SDK--you don't need to use the legacy DirectX SDK at all. You can find Direct3D 11 supporting replacements for all the deprecated D3DX library functionality as well.
MSDN
Where is the DirectX SDK (2015 Edition)?
Living without D3DX
DirectX SDK Samples Catalog
DirectX SDK Tools Catalog
There are indeed numerous resources online for learning Direct3D 11. Keep in mind that many of the Direct3D 11 learning resources were written prior to the deprecation of the legacy DirectX SDK, so they tend to focus on deprecated support code like D3DX11. I'd recommend starting with the DirectX Tool Kit for DirectX 11 tutorials, and once you work through those you can go back to resources like the rastertek.com tutorials knowing what's deprecated and what's not.
Getting Started with Direct3D 11
Book Recommendations

Direct3D 12 is also supported on Windows 10, Xbox One, and for the Universal Windows Platform, but it's an expert API that assumes you are already an expert on Direct3D 11. See Getting Started with Direct3D 12 and DirectX Tool Kit for DirectX 12.
Direct3D 10.x is fully replaced by Direct3D 11. There's no need to use Direct3D 10.x at all on any platform. Direct3D 11 supports all the Direct3D 10.x era hardware and more through the Direct3D hardware Feature Level mechanism, and is available on all supported versions of Windows that had Direct3D 10.x.
Direct3D 9 is a legacy API, and while its still supported for application compatibility purposes, a lot of the behavior is emulated on modern versions of the OS. Debugging and development support for Direct3D 9 on modern versions of Windows is minimal. Furthermore, the only place to get samples and utility libraries for Direct3D 9 is the legacy DirectX SDK. The only case where it makes sense to use Direct3D 9 for an application is if you have to target Windows XP Service Pack 3 or Windows Server 2003 Service Pack 2. See this post for some important information on this scenario.
Answer: you can find the webpage and code sample data at wayback machine:
https://web.archive.org/web/20161003152649/http://www.codesampler.com/dx9src.htm


what is meant by biased and unbiased Autocovariance sequence estimate?

Question: In nonparametric spectral estimation method what is meant by biased and unbiased Autocovariance sequence estimate and why most commonly biased one is used?
I have the answer to the second question from Peter Stoica (SPECTRAL ANALYSIS OF SIGNALS)but not getting what he wants to say.
Answer: In spectral estimation, one estimates "spectra" and other values. And one is interested in knowing whether the estimate $\hat{x}$ converge to the "true" but unknown value  $x$. It is unknown, for instance because one has only access to a finite quantity $N$ of samples to compute with, a limited number of realization, because ergodicity is not assured, etc. So we want to know whether  $\hat{x}_N\to x$ as $N\to \infty$. The convergence can be thought in different ways, and the most common is the mean square sense: does
$$\lim_{N\to \infty} E(|\hat{x}_N-x|^2)=0$$
where $E$ is the expectation? This can be really complicated to prove in practice. Thus, often people are satisfied when simpler conditions are met. And there are two necessary conditions for the above:
$$\lim_{N\to \infty} E(\hat{x}_N)=x$$
$$\lim_{N\to \infty} E(|\hat{x}_N|^2)=0$$
The first is the asymptotic unbiasedness, the second the vanishing variance. Together, they define consistent estimators. So, a biased autocorrelation estimate won't converge to the true autocorrelation. And derived estimators (like periodograms) are unlikely to converge as well.
Comment: thanks, Laurent Duval I m getting at least some intuition ,thanks once again
Answer: Just for the sake of offering a different perspective, here's a basic explanation that tries to give some intuition without any theory.
Let's assume we have $N$ samples of a zero-mean random process $x(n), n=0...N-1$ and we want to estimate $R(d)=E(x(n)x^*(n-d))$.  One obvious approach is to average $x(n)x^*(n-d)$ for all the data that we have:
$$\hat{R}(d)=\frac{1}{N-d}\sum_{n=d}^{N-1}{x(n)x^*(n-d)}$$
This is an unbiased estimate because it will converge to the true value as you use more and more data (larger $N$).  But the estimates for larger lags $d$ will be less accurate than the estimates for smaller lags because we have less data available on which to base the estimates for the large lags.
Another approach is just to normalize the estimate by $1/N$ every time:
$$\hat{R}(d)=\frac{1}{N}\sum_{n=d}^{N-1}{x(n)x^*(n-d)}$$
This is a biased estimate because it does not converge to the true value, even when you use a lot of data.  The estimates for larger lags $d$ are based on $N-d$ samples, but we normalize by $1/N$ regardless of the lag, so the estimates are a little too small.  But the less accurate estimates (those with larger lags) are attenuated relative to the more accurate estimates (those with smaller lags), which can help.  It is also often easier to compute: in fact, periodogram estimators (such as those that use the DFT) can be seen as using a biased autocorrelation.
Comment: Estimates that are biased for fixed $N$ but unbiased in the limit as $N$ goes to infinity are *asymptotically unbiased* rather than simply *unbiased*.


How to use the Front Page module

Question: I am currently trying to make my front page viewable by anonymous users, I am using the Front Page module to do this in Drupal 8, however I am unsure how to use it?
Comment: Does this really require a module?
Comment: I'm using this one https://www.drupal.org/project/front
Comment: Sorry, I misread what you said earlier and apparently so, unless you know another way?
Comment: You can set any Node as the front page in the site settings. You can also create a View page and set that too. I'm just not sure why a module is needed for this.
Comment: Sorry I'm very new to Drupal, so i'm struggling. Permission settings are still not allowing the anonymous user to just view the home page.
Comment: Then there is some config or module altering that behavior because vanilla Drupal does not restrict front page access to anonymous users by default.
Answer: The default front page Drupal uses is a view which lists several pieces of content (nodes). This view is by default visisble for authenticated and anonymous users and you do not require a module for it.
The front page module is only useful if you want to show a different page to users depending on their role. For instance you can configure the front page anonymous user to be /anon-front and for authenticated user /auth-front. It does not do anything with permissions but simply redirects the user when they click the home link.
In your case it seems that anonymous users are not able to see the default front page. There are two likely reasons for this:

All your nodes are private and anonymous users are not allowed to view any nodes.
The views configuration has been altered and the view is only visible for authenticated users.

You do not need to use the front page module (at least not the way the question is currently written), but without further information we cannot help you debug either.
Answer: If I recall correctly, you can go to the configuration page, and in the anonymous users section, you can choose 'alias'.
-- edit --
I just installed the D8 version of the module. It's a little different from D7, probably because it's still an alpha version and incomplete.
Go to Admin -> Configuration -> Front Page -> settings
Under "Front page for anonymous user", check 'enable', and enter the path to the page you want anonymous users to see.
I don't know if it will work or not though, since it's an alpha version, it may not be ready for usage.
Comment: There is not an option for this. I'm still struggling to allow anonymous users to view the home page.
Comment: I edited my answer.

How to use the Front Page module


Dialectics and Machiavelli

Question: What is the relation between Marxist dialectics and Machiavelli's philosophy? I have read Lefort, and he seems good, but I was unsure if he was an academic playing games.
Comment: To Marxists, Lefort is a heretic, see [Erfani, Fixing Marx with Machiavelli](https://www.tandfonline.com/doi/10.1080/00071773.2008.11006642). Althusser is another post-Marxist author who connected Machiavelli to Marx's dialectic, see [Bargu's chapter Machiavelli after Althusser](https://brill.com/view/book/edcoll/9789004287686/B9789004287686_024.xml), so did Gramsci.
Comment: cheers @Conifold i have an unread book on althusser
Answer: I would have to say that it is a stretch of the historical and philosophical imaginations to compare or relate Marxian Dialectics with Machiavellian Power.
Karl Marx's philosophy, specifically, his Dialectical Philosophy-(a.k.a. "Dialectical Materialism"), was the complete "antithesis" of Machiavelli's Prince or Supreme Ruler. Marx detested the consolidation of Power. be it singularly held power, such as State or Capitalistic Tyranny or the Power of the Bureaucratic or Capitalistic classes.  Marx's "Dictatorship of the Proletariat", was a temporary phase within his Dialectical process that would ultimately lead to a Communist Utopia.  The Dialectical revolution would have initially consisted of the complete eradication of traditional political (and especially Capitalistic) hierarchies, followed by the fulfillment of Universal equality and freedom. The radically anti-hierarchical, pro-Utopian  philosophy of Karl Marx, was absolutely antithetical to Machiavelli's Prince.
400 years earlier, Nicolo Machiavelli, pioneered a Political Philosophy that "justified" the historical and sobering reality of power.  Machiavelli, was the furthest thing from being a Political Idealist and probably would have scoffed at Marx's juvenile sounding language.  The Prince, was the starting and ending point of the State; the citizens (or subjects) in a Machiavellian world, were of a secondary or even tertiary nature.  While Machiavelli was an accomplished Philosopher and Writer-(though apparently, not a very good Politician or Diplomat), Dialectics, would have been viewed by him as "classically" related subject matter and not a contemporaneous subject matter.  However, if such a Dialectically inspired fantasy, such as a Marxian Communist revolution or social transformation, showed early signs of success, Machiavelli's Prince would have crushed that early sign of success, "at the blink of an eye".

Dialectics and Machiavelli


"They are there." and "They're there." versus "There they are." and "There they're."

Question: Are any of the phrases in the title incorrect in any way? Do the meanings differ in any way? Is one preferred over the other and if so then why? I find this particularly interesting for many reasons including because a listener can not distinguish whether a speaker said "There they're." or "They're there." Also, are there other more complex and/or more interesting examples of this kind?
Comment: A string walks into a bar and says to the bartender, "Gimme a drink."  The bartender says, "Sorry, we don't serve strings in here."  The string goes outside and sees a guy walking toward him.  He says to the guy, "Come here, can you do me a favor?  Can you frazzle my ends up a bit then loop me around and stick my head through the loop and and pull it tight?"  The guy shrugs and does it.  The string goes back into the bar and right up to the bartender and says, "Gimme a drink"  The bartender says,  'Hey aren't you that string that was in here earlier?"  The string says, "Nope, I'm frayed knot."
Answer: "There they're" is nonstandard English. Contractions of be, had, and would cannot appear at the end of a clause. They can only appear as unstressed sentence elements, and inverting the sentence order in this way (called stranding) puts stress on the verb. This avoids any ambiguity with "They're there," for this particular case.
Just as it changes the grammatical stress, inverting the word order also changes the sentence's semantic stress, emphasizing there instead of they, answering slightly different questions:

Did the Joneses go to the party? – Yes, they are there.
Where are the Joneses? – Oh, there they are!


Locked Mac find my Mac

Question: Find my Mac is locked I wanted to know if there is a way to rebuild a Mac with find my Mac being locked to an Apple ID. I can't remember what I put for my 6 digit pin. Also, is there a way to just get back into it so I can back up my information.
Comment: The first thing to do is unlock it again from iCloud, on any web browser. If you can't remember your iCloud details, start at https://iforgot.apple.com
Answer: You need to visit an Apple Store (Genius Bar appointment) to get it unlocked.
https://support.apple.com/en-us/HT204756

How do I unlock my Mac?
Once you locate your Mac, you can unlock it by
entering your passcode on the lock screen. If you forget your
passcode, you'll need to take your Mac to an Apple Authorized Service
Provider along with your proof of purchase.

Locked Mac find my Mac


Why omit "Av harachamim" for the four parashiyos?

Question: "Av harachamim" is a prayer asking God to recall those who died al kidush hashem. It was written in response to the First Crusade (and is thus said only in the Ashk'nazi rite). Because of its somber topic (or origin), it is omitted on various joyous occasions, though which occasions qualify varies widely. It is also, according to some views (cited in Mishna B'rura 685) and in many synagogues, omitted when the "four parashiyos" are read. Why omit it when the "four parashiyos" are read? That's not a particularly joyous occasion.
Comment: kind of related: http://judaism.stackexchange.com/questions/29300/why-skip-yikum-purkan-and-mi-sheberach-on-a-weekday-yom-tov?rq=1
Comment: I always assumed that the reason was because the four parshiyos represent a time of celebration (due to the 'redemption' period of Adar and Nissan, as per Rashi Taanis 29a). Even though this is true of the entire month of Adar, on the week(s) without special parshiyos its celebratory period isn't expressed, so we don't need to suppress the spirit-dampering prayer of Av Harachamim
Comment: But I bet if you check the Nittei Gavriel or Piskei Teshuvos he gives answers... no?
Answer: First of all, it should be noted that there is a custom to say "Av Harachamim" on the four Parshios-Shabbosos as well. The custom not to say it is in the Darkei Moshe in the name of the Maharail (Siman 685), and seems to be the custom of the Magen Avraham and R. Yaakov Lorberbaum of Lissa (in his Siddur, Derech Hachayim). However, the Eliyah Rabba (685:18) and Shaarei Efraim there mention the custom to say Av Harachamim even during the 4 parshios.
However, the Aruch Hashulchan (685:9) seems to approve of the custom to omit the prayer, because these Shabbosos have a festive air about them, just like the Shabbos Mevarchim.1 It sounds like anytime when something special is done regarding the leining, there's a feeling of happiness (because there are more kibbudim to be given out if there's another Sefer Torah, maybe? I'm not sure).
R' Yaakov Emden (Mor Uktziah 685:10) writes that once Adar has entered, "מרבים בשמחה", we increase our joy, and don't want to dampen that joy with the somber prayer of Av Harachamim.2 (Even though there are week(s) in Adar without an extra parsha, I assume that this isn't an issue because the festive nature of the month isn't express in any halacha during that week/weeks)
My understanding has always been that these parshiyos are related to the holidays around which they are centered (Purim and Pesach), and so the season, at least on a Shabbos when that feeling is being expressed by the "four parshiyos", should be a joyous one.

1 "ולעניות דעתי נראה שלא לומר כיון שאין מזכירין נשמות והם שבתות של שמחה ולא גריעי משבת שמברכין בו את החודש"
2 "במגן אברהם הביא בשם מהרי״ל שבכל ד׳ פרשיות אין מזכירין נשמות… לא נודע לי טעם בפרשת שקלים אבל בפרשת זכור שכבר נכנס אדר שמרבין בשמחה נ״ל שנכון מנהג מהרי״ל וכ״ש בשתי פרשיות שלאחר פורים שהם בין גאולה לגאולה דהוי מנהגא"
Comment: I would also add that skipping Av Harachamim on Shabbos Zachor just sounds strange.
Answer: Mishna Berura 685:18 actually brings a dispute as to whether we say Av HaRachamim during the weeks of the 4 Parshios. Minhag Chabad is to say on Parshas Zachor and on Parshas Para מפורש בלוח 'היום-יום' לש"פ זכור ופרה שאומרים 'אב הרחמים', however do not say it on Parshas Shekalim or HaChodesh since we are either Bentching Rosh Chodesh or it is Rosh Chodesh.
I have yet to see a reason mentioned anywhere for those that do not say it - other than "we do not say it". My own thought is perhaps there is increased Simcha in taking out a second Sefer Torah.
Comment: @gt6989b Well, the answer spends half the time discussing opinions the OP deliberately excluded, and the other half speculating.
Comment: I wonder what the -1 was for -- seems reasonable answer to me. In general it is a strange practice to downvote without explanation...
Comment: @gt6989b http://meta.judaism.stackexchange.com/a/146
Answer: Those that omit Av Harachamim do so because the Four Parshios are to some extent celebratory, in that they usher in and remind us about the oncoming festival of Pesach.  The poskim failed to make this explicit because they mistakenly presume that the reader would realize this on his or her own.  Of course, my assertion is, by its very nature, difficult to prove.
Comment: Thanks for your answer and welcome to Mi Yodeya. I hope you stick around and enjoy the site. Please consider [registering](http://judaism.stackexchange.com/users/login) your account, which will [give you access](http://meta.stackexchange.com/q/44557) to more of the site's features.


買う、買い取りする、買い取る what is the difference?

Question: I'm a bit lost on all the ways to say "to buy". Can anyone help me understand the difference? According to my research it seems that 買い取りする and 買い取る are used when the shop buys something for the customer, like a notion of trade, but I'm not sure of that and I don't understand the difference between the する version and the non-する one. If you can give me some examples to understand it, it would be nice :)
Thank you
Answer: 買い取る probably emphasizes that you make the item yours, e.g. 別荘を買取る.
On the other hand, for 買取 (or 買い取りする),  it can refer to companies buying used goods from you. For example, if you have an unneeded computer, you may want to search "パソコン 買取".
Comment: Thank you for your reply ! It's much more clear. Just one last clarification : what's the nuance in term of meaning between 別荘を買い取る and 別荘を買取する ?

買う、買い取りする、買い取る what is the difference?


What are variational autoencoders and to what learning tasks are they used?

Question: As per this and this answer, autoencoders seem to be a technique that uses neural networks for dimension reduction. I would like to additionally know what is a variational autoencoder (its main differences/benefits over a "traditional" autoencoders) and also what are the main learning tasks these algorithms are used for.
Answer: Even though variational autoencoders (VAEs) are easy to implement and train, explaining them is not simple at all, because they blend concepts from Deep Learning and Variational Bayes, and the Deep Learning and Probabilistic Modeling communities use different terms for the same concepts. Thus when explaining VAEs you risk either concentrating on the statistical model part, leaving the reader without a clue about how to actually implement it, or vice versa to concentrate on the network architecture and loss function, in which the Kullback-Leibler term seems to be pulled out of thin air. I'll try to strike a middle ground here, starting from the model but giving enough details to actually implement it in practice, or understand someone's else implementation.
VAEs are generative models
Unlike classical (sparse, denoising, etc.) autoencoders, VAEs are generative models, like GANs. With generative model I mean a model which learns the probability distribution $p(\mathbf{x})$ over the input space $\mathcal{x}$. This means that after we have trained such a model, we can then sample from (our approximation of) $p(\mathbf{x})$. If our training set is made of handwritten digits (MNIST), then after training the generative model is able to create images which look like handwritten digits, even though they're not "copies" of the images in the training set.
Learning the distribution of the images in the training set implies that images which look like handwritten digits should have an high probability of being generated, while images which look like the Jolly Roger or random noise should have a low probability. In other words, it means learning about the dependencies among pixels: if our image is a $28\times 28=784$ pixels grayscale image from MNIST, the model should learn that if a pixel is very bright, then there's a significant probability that some neighboring pixels are bright too, that if we have a long, slanted line of bright pixels we may have another smaller, horizontal line of pixels above this one (a 7), etc.
VAEs are latent variable models
The VAE is a latent variables model: this means that $\mathbf{x}$, the random vector of the 784 pixel intensities (the observed variables), is modeled as a (possibly very complicated) function of a random vector $\mathbf{z}\in\mathcal{Z}$ of lower dimensionality, whose components are unobserved (latent) variables. When does such a model make sense? For example, in the MNIST case we think that the handwritten digits belong to a manifold of dimension much smaller than the dimension of $\mathcal{x}$, because the vast majority of random arrangements of 784 pixel intensities, don't look at all like handwritten digit. Intuitively we would expect the dimension to be at least 10 (the number of digits), but it's most likely larger because each digit can be written in different ways. Some differences are unimportant for the quality of the final image (for example, global rotations and translations), but others are important. So in this case the latent model makes sense. More on this later. Note that, amazingly, even if our intuition tells us that the dimension should about 10, we can definitely use just 2 latent variables to encode the MNIST dataset with a VAE (though results won't be pretty). The reason is that even a single real variable can encode infinitely many classes, because it can assume all possible integer values and more. Of course, if the classes have significant overlap among them (such as 9 and 8 or 7 and I in MNIST), even the most complicated function of just two latent variables will do a poor job of generating clearly discernible samples for each class. More on this later.
VAEs assume a multivariate parametric distribution $q(\mathbf{z}\vert\mathbf{x},\boldsymbol{\lambda})$ (where $\boldsymbol{\lambda}$ are the parameters of $q$), and they learn the parameters of the multivariate distribution. The use of a parametric pdf for $\mathbf{z}$, which prevents the number of parameters of a VAE to grow without bounds with the growth of the training set, is called amortization in VAE lingo (yeah, I know...).
The decoder network

We start from the decoder network because the VAE is a generative model, and the only part of the VAE which is actually used to generate new images is the decoder. The encoder network is only used at inference (training) time.
The goal of the decoder network is to generate new random vectors $\mathbf{x}$ belonging to the input space $\mathcal{X}$, i.e., new images, starting from realizations of the latent vector $\mathbf{z}$. This means clearly that it must learn the conditional distribution $p(\mathbf{x}\vert\mathbf{z})$. For VAEs this distribution is often assumed to be a multivariate Gaussian1:
$$p_{\boldsymbol{\phi}}(\mathbf{x}\vert\mathbf{z}) = \mathcal{N}(\mathbf{x}|\boldsymbol{\mu}(\mathbf{z}; \boldsymbol{\phi}), \boldsymbol{\sigma}(\mathbf{z}; \boldsymbol{\phi})^2I) $$
$\boldsymbol{\phi}$ is the vector of weights (and biases) of the encoder network. The vectors $\boldsymbol{\mu}(\mathbf{z};\boldsymbol{\phi})$ and $\boldsymbol{\sigma}(\mathbf{z}; \boldsymbol{\phi})$ are complex, unknown nonlinear functions, modeled by the decoder network: neural networks are powerful nonlinear functions approximators.

As noted by @amoeba in the comments, there is a striking similarity between the decoder and a classic latent variables model: Factor Analysis. In Factor Analysis, you assume the model:
$$ \mathbf{x}\vert\mathbf{z}\sim\mathcal{N}(\mathbf{W}\mathbf{z}+\boldsymbol{\mu}, \boldsymbol{\sigma}^2I),\ \mathbf{z}\sim\mathcal{N}(0,I)$$
Both models (FA & the decoder) assume that the conditional distribution of the observable variables $\mathbf{x}$ on the latent variables $\mathbf{z}$ is Gaussian, and that the $\mathbf{z}$ themselves are standard Gaussians. The difference is that the decoder doesn't assume that the mean of $p(\mathbf{x}|\mathbf{z})$ is linear in $\mathbf{z}$, nor it assumes that the standard deviation is a constant vector. On the contrary, it models them as  complex nonlinear functions of the $\mathbf{z}$. In this respect, it can be seen as nonlinear Factor Analysis. See here for an insightful discussion of this connection between FA and VAE. Since FA with an isotropic covariance matrix is just PPCA, this also ties in to the well-known result that a linear autoencoder reduces to PCA.

Let's go back to the decoder: how do we learn $\boldsymbol{\phi}$? Intuitively we want latent variables $\mathbf{z}$ which maximize the likelihood of generating the $\mathbf{x}_i$ in the training set $D_n$. In other words we want to compute the posterior probability distribution of the $\mathbf{z}$, given the data:
$$p(\mathbf{z}\vert\mathbf{x})=\frac{p_{\boldsymbol{\phi}}(\mathbf{x}\vert\mathbf{z})p(\mathbf{z})}{p(\mathbf{x})}$$
We assume a $\mathcal{N}(0,I)$ prior on $\mathbf{z}$, and we're left with the usual issue in Bayesian inference that computing $p(\mathbf{x})$ (the evidence) is hard (a multidimensional integral). What's more, since here $\boldsymbol{\mu}(\mathbf{z};\boldsymbol{\phi})$ is unknown, we can't compute it anyway. Enter Variational Inference, the tool which gives Variational Autoencoders their name.
Variational Inference for the VAE model
Variational Inference is a tool to perform approximate Bayesian Inference for very complex models. It's not an overly complex tool, but my answer is already too long and I won't go into a detailed explanation of VI. You can have a look at this answer and the references therein if you're curious:
https://stats.stackexchange.com/a/270569/58675
It suffices to say that VI looks for an approximation to $p(\mathbf{z}\vert \mathbf{x})$ in a parametric family of distributions $q(\mathbf{z}\vert \mathbf{x},\boldsymbol{\lambda})$, where, as noted above, $\boldsymbol{\lambda}$ are the parameters of the family. We look for the parameters which minimize the Kullback-Leibler divergence between our target distribution $p(\mathbf{z}\vert \mathbf{x})$ and $q(\mathbf{z}\vert \mathbf{x},\boldsymbol{\lambda})$:
$$\min_{\boldsymbol{\lambda}}\mathcal{D}[p(\mathbf{z}\vert \mathbf{x})\vert\vert q(\mathbf{z}\vert \mathbf{x},\boldsymbol{\lambda})]$$
Again, we cannot minimize this directly because the definition of Kullback-Leibler divergence includes the evidence. Introducing the ELBO (Evidence Lower BOund) and after some algebraic manipulations, we finally get at:
$$ELBO(\boldsymbol{\lambda})= E_{q(\boldsymbol{z}\vert \mathbf{x},\boldsymbol{\lambda})}[\log p(\mathbf{x}\vert\boldsymbol{z})]-\mathcal{D}[(q(\boldsymbol{z}\vert \mathbf{x},\boldsymbol{\lambda})\vert\vert p(\boldsymbol{z})]$$
Since the ELBO is a lower bound on evidence (see the above link), maximizing the ELBO is not exactly equivalent to maximizing the likelihood of data given $\boldsymbol{\lambda}$ (after all, VI is a tool for approximate Bayesian inference), but it goes in the right direction.
In order to make inference, we need to specify the parametric family $q(\boldsymbol{z}\vert \mathbf{x},\boldsymbol{\lambda})$. In most VAEs we choose a multivariate, uncorrelated Gaussian distribution
$$q(\mathbf{z}\vert \mathbf{x},\boldsymbol{\lambda}) = \mathcal{N}(\mathbf{z}\vert\boldsymbol{\mu}(\mathbf{x}), \boldsymbol{\sigma}^2(\mathbf{x})I) $$
This is the same choice we made for $p(\mathbf{x}\vert\mathbf{z})$, though we may have chosen a different parametric family. As before, we can estimate these complex nonlinear functions by introducing a neural network model. Since this model accepts input images and returns parameters of the distribution of the latent variables we call it the encoder network.
The encoder network
Also called the inference network, this is only used at training time.

As noted above, the encoder must approximate $\boldsymbol{\mu}(\mathbf{x})$ and  $\boldsymbol{\sigma}(\mathbf{x})$, thus if we have, say, 24 latent variables, the output of the encoder is a $d=48$ vector. The encoder has weights (and biases) $\boldsymbol{\theta}$. To learn $\boldsymbol{\theta}$, we can finally write the ELBO in terms of the parameters $\boldsymbol{\theta}$ and $\boldsymbol{\phi}$ of the encoder and decoder network, as well as the training set points:
$$ELBO(\boldsymbol{\theta},\boldsymbol{\phi})= \sum_i E_{q_{\boldsymbol{\theta}}(\boldsymbol{z}\vert \mathbf{x}_i,\boldsymbol{\lambda})}[\log p_{\boldsymbol{\phi}}(\mathbf{x}_i\vert\boldsymbol{z})]-\mathcal{D}[(q_{\boldsymbol{\theta}}(\boldsymbol{z}\vert \mathbf{x}_i,\boldsymbol{\lambda})\vert\vert p(\boldsymbol{z})]$$
We can finally conclude. The opposite of the ELBO, as a function of $\boldsymbol{\theta}$ and $\boldsymbol{\phi}$, is used as the loss function of the VAE. We use SGD to minimize this loss, i.e., maximize the ELBO. Since the ELBO is a lower bound on the evidence, this goes in the direction of maximizing the evidence, and thus generating new images which are optimally similar to those in the training set. The first term in the ELBO is the expected negative log-likelihood of the training set points, thus it encourages the decoder to produce images which are similar to the training ones. The second term can be interpreted as a regularizer: it encourages the encoder to generate a distribution for the latent variables which is similar to $p(\boldsymbol{z})=\mathcal{N}(0,I)$. But by introducing the probability model first, we understood where the whole expression comes from: the minimization of the Kullabck-Leibler divergence between the approximate posterior $q_{\boldsymbol{\theta}}(\boldsymbol{z}\vert \mathbf{x},\boldsymbol{\lambda})$ and the model posterior $p(\boldsymbol{z}\vert \mathbf{x},\boldsymbol{\lambda})$.2
Once we have learned $\boldsymbol{\theta}$ and $\boldsymbol{\phi}$ by maximizing $ELBO(\boldsymbol{\theta},\boldsymbol{\phi})$, we can throw away the encoder. From now on, to generate new images just sample $\boldsymbol{z}\sim \mathcal{N}(0,I)$ and propagate it through the decoder. The decoder outputs will be images similar to those in the training set.
References and further reading

the original paper: Auto-Encoding Variational Bayes
a nice tutorial, with a few minor imprecisions: Tutorial on Variational Autoencoders
how to reduce the blurriness of the images generated by your VAE, while at the same time getting latent variables which have a visual (perceptual) meaning, so that you can "add" features (smile, sunglasses, etc.) to your generated images: Deep Feature Consistent Variational
Autoencoder
improving the quality of VAE-generated images even more, by using Gaussian versions of autoregressive autoencoders:Improved Variational Inference
with Inverse Autoregressive Flow
new directions of research and a deeper understanding of pros & cons of the VAE model: Towards a Deeper Understanding of Variational Autoencoding Models & INFERENCE SUBOPTIMALITY
IN VARIATIONAL AUTOENCODERS

1 This assumption is not strictly necessary, though it simplifies our description of VAEs. However, depending on applications, you may assume a different distribution for $p_{\phi}(\mathbf{x}\vert\mathbf{z})$. For example, if $\mathbf{x}$ is a vector of binary variables, a Gaussian $p$ makes no sense, and a multivariate Bernoulli can be assumed.
2 The ELBO expression, with its mathematical elegance, conceals two major sources of pain for the VAE practitioners. One is the average term $E_{q_{\boldsymbol{\theta}}(\boldsymbol{z}\vert \mathbf{x}_i,\boldsymbol{\lambda})}[\log p_{\boldsymbol{\phi}}(\mathbf{x}_i\vert\boldsymbol{z})]$. This effectively requires computing an expectation, which requires taking multiple samples from $q_{\boldsymbol{\theta}}(\boldsymbol{z}\vert \mathbf{x}_i,\boldsymbol{\lambda})$. Given the sizes of the involved neural networks, and the low convergence rate of the SGD algorithm, having to draw multiple random samples at each iteration (actually, for each minibatch, which is even worse) is very time-consuming. VAE users solve this problem very pragmatically by computing that expectation with a single (!) random sample. The other issue is that to train two neural networks (encoder & decoder) with the backpropagation algorithm, I need to be able to differentiate all steps involved in forward propagation from the encoder to the decoder. Since the decoder is not deterministic (evaluating its output requires drawing from a multivariate Gaussian), it doesn't even make sense to ask if it's a differentiable architecture. The solution to this is the reparametrization trick.
Comment: +6. I put a bounty here, so hopefully you will get some additional upvotes. If you want to improve something in this post (even if only formatting), now is a good time: every edit will bump this thread to the front page and make more people pay attention to the bounty. Apart from that, I was thinking a bit more on the conceptual relationship between EM estimation of the FA model and VAE training. You link to the lecture slides that goes into great length about how VAE training is similar to EM, but it could be great to distill some of that intuition into this answer.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](http://chat.stackexchange.com/rooms/73096/discussion-on-answer-by-deltaiv-what-are-variational-autoencoders-and-to-what-le).
Comment: (I did some reading on that, and I am thinking of writing an "intuitive/conceptual" answer here focusing on FA/PPCA <--> VAE correspondence in terms of EM <--> VAE training, but I don't think I know enough for an authoritative answer... So I'd much rather somebody else wrote it :-)
Comment: Thanks for the bounty! Some major edits implemented. I won't address the EM stuff, though, because I don't know enough about EM, and becase I have enough time (you know how long it takes me to implement major edits...;-)
Comment: the inference in the context of VAE is NOT that prediction process against model training for deep learning...
Answer: Variational Auto Encoders are an intersection between Auto-Encoders Neural Networks and Variational Inference. It was introduced as an application for a general purpose VI using the reparameterization trick in a paper from 2014 by Kingma and Welling. The main goal is to generate more data - by creating a more regularized latent space for auto encoders.
Auto Encoders
Auto Encoders (AEs) are a NN architecture used mainly to compress data / dimensionality reduction. It's made of two NNs - an Encoder $f_\phi(x)$ which encodes the original data $x$ to some latent space $z$. And a Decoder $g_{\theta}(z)$which decodes the latent space back to the data space. $f$ is parameterized by the NN weights $\phi$, and $g$ is parameterized by $\theta$. The overall structure looks like this:

In order to optimize the NN, you can take, e.g., the L2 norm of the difference between the original data $x$ and the reconstructed data $\hat  x = g(f(x))$: $Loss = ||x-\hat x||^2_2$. As usual in NN, you optimize the weights by some form of Gradient Descent (e.g., SGD, ADAM etc.). Once the weights have been optimized, the outputs of the encoder and decoder are fixed - for a given $x$ you will always get the same $z=f(x)$, and for a given $z$ you will always get the same $x=g(z)$.
Now, you would think that this could also be used for generation of new data: sample some random points in the $z$ space, pass them through the decoder, and get new data. Turns out it doesn't work so well - the reason being is that the process of optimizing AEs only care about your actual data, and it doesn't care how it's going to store the representation of the data in the latent $z$ space. So the $z$ space becomes very "messy".
Variational Inference
Variational Inference (VI) is a method to find an approximation to intractable posteriors. Given Bayes formula:
$$ p(z|x) = \frac{p(x|z)p(z)}{\int p(x|z)p(z)dz}
$$
The numerator consists of the likelihood $p(x|z)$ and the prior $p(z)$, both are usually known. The denominator (which is actually equal to $=p(x)$) is called the "evidence", and in high dimensions its usually hard to impossible to compute. Although it's only a normalizing constant (given the data is known) without it we don't really know the distribution. VI says - let's place a probability we know and can control its parameters $q_\phi(z) = q_\phi(z|x)$ (e.g., Gaussian) and "turn the knobs" of that distribution (=optimize the parameters $\phi$) until we reach something that looks like the true posterior. Since we don't know the true posterior, only up to a normalizing constant - a special metric is used, the KL divergence, which is a metric to measure the "statistical distance" between two distributions:
$$KL(q(z)||p(z|x)) = \int q(z)\log\frac{q(z)}{p(z|x)}dz
$$
By using that metric, we can ignore the evidence, and only optimize the terms we know and care about (whose negative is called the ELBO [=evidence lower bound] - hence minimizing the KL is equivalent to maximizing the ELBO):
$$ =  \int q(z)\log q(z)dz - \int q(z)\log p(z|x)dz = \mathbb E_{q}[\log q(z)]-\int q(z)\log \frac{p(x|z)p(z)}{p(x)}dz \\
= \mathbb E_{q}[\log q(z)] - \mathbb E_{q}[\log p(x|z)p(z)]+\log p(x) \\
ELBO = \mathbb E_{q}[\log p(x|z)p(z)] - \mathbb E_{q}[\log q(z)]
$$
There are a few ways to continue here - up to the paper the main approach was Coordinate Ascent VI with the "mean field" assumption. There was also the approach of doing gradient ascent on the ELBO, by the log-derivative trick, which suffered from high variance (although later, variance reduction techniques were used. E.g., BBVI). The main focus of the paper seems to be the new method they suggested which is the reparameterization trick (later also used in ADVI): sample from some neutral distribution that doesn't depend on the parameters of the variational distribution $\phi$, and transform those samples to samples from $q_\phi$ - then evaluate the gradient for those samples, and take their average (Monte Carlo estimate):
$$ \epsilon \sim p'(\epsilon) \\
z = \mathcal T(\epsilon; \phi) \\
\nabla _\phi ELBO \approx \frac{1}{L}\sum_{l=1}^L \nabla _\phi [\log p(x|T(\epsilon; \phi))p(T(\epsilon; \phi))] -\log q(T(\epsilon; \phi))]
$$
Variational Auto Encoders
We now place distributions over $z$ and $x$ - e.g., suppose $p(x|z)$ is a Gaussian (though it can also model discrete data and be Bernoulli or Categorical). If we look at the decoder structure from before and say that now it outputs the parameters of that Gaussian $\mu_\theta, \Sigma_\theta$ [suppose for illustration's sake that the decoder is fixed and its weights $\theta$ are known], the posterior $p(z|x)$ is intractable, because of the decoder NN function (a complex non-linear function).
So we can do VI to recover it. And suppose we decide to place also a Gaussian $q(z|x)=N(\mu,\Sigma)$. But suppose we don't simply use global parameters $\phi = (vec(\mu), vec(\Sigma))$, but instead place an encoder network that will output the mean and covariance: $\mu_\phi, \Sigma_\phi$. The overall structure now looks like this:

Suppose we also take a standard Gaussian prior over the $z$'s: $p(z)=N(0,I)$. In this case, we can "massage" the ELBO a little bit more:
$$ ELBO = \mathbb E_{q}[\log p(x|z)p(z)] - \mathbb E_{q}[\log q(z)] = \mathbb E_{q}[\log p(x|z) + \log p(z) - \log q(z)] \\
= -KL(q_\phi(z|x)||p(z)) + \mathbb E_{q_\phi}[\log p_\theta(x|z)]
$$
The reason to do so is that in this case this KL has a closed form. Assuming we have a closed form for the KL, we can also use Monte Carlo estimates (using the reparameterization trick) for the 2nd term:
$$ = -KL(q_\phi(z|x)||p(z)) + \frac{1}{L}\sum_{l=1}^L \log p_\theta(x|z=\Sigma^{0.5}_\phi\cdot\epsilon_l +\mu_\phi)
$$
Note that the 1st part of the objective is optimized only w.r.t. $\phi$, and the 2nd error is optimized both w.r.t. $\phi$ (encoder) and w.r.t. $\theta$ (decoder). There are 2 ways to look at this loss:

Looking at the loss terms, noticing that the 2nd term (called the reconstruction term) is very similar to a loss of AEs (and actually equivalent [w.r.t. $\arg \max$] to it if we assume $\Sigma_\theta=I$, and $\hat x = \mu_\theta$). The 1st term acts as a sort of a regularizer, which tells the (approximated) posterior to not stretch too far from a standard Gaussian.

Looking at the derivatives. For illustration's sake suppose we are actually separating the update rule into two: Suppose $\phi$ is fixed, $\nabla_\theta ELBO$ is finding the decoder by doing a sort of maximum likelihood on our data (given $z$'s drawn from the posterior). Suppose $\theta$ is fixed, $\nabla_\phi ELBO$ is finding the encoder by approximating the posterior using VI.

So, this is not strictly a VI method, as in VI you usually assume the likelihood is fixed. Here you have two moving parts: you optimize the likelihood (decoder) and optimize the posterior (encoder) simultaneously.
Using VAE eventually leads to a latent space which is more ordered and tries to be more like a standard Gaussian.
I've made a video about this topic on my YouTube channel (which elaborates a bit on the paper and on VI), if you want to learn more.


Is it possible to return to normal mode in the middle of a vim command?

Question: By simply calling :(range)g/bob/norm Axxx I can add xxx to the to the end of all lines in range containing bob. Is there a way to return to normal mode after having used A/I/a/i to enter insert  mode, all within a command, in order to perform more actions to the matching lines without starting another command?
Comment: `:help :bar` seems to be what you what to read
Comment: @user642832 So? Did my answer help?
Answer: Let's say that we're using the global command to surround each matching line with brackets. (This is not really a good way to bracket text. It's just for illustration here.)
You hinted at maybe inserting an Esc somewhere in there. Perhaps like this...
:g/bob/ norm! A}<ESC>I{

But that approach won't work.
Others might have a first instinct to try something like this:
:g/bob/ norm! A} | norm! I{

Alas, this won't work either. Both these cases see everything after the opening A as text to be appended.
Digging deeper into the second approach, if we look at :h :norm we'll find the following:

This command cannot be followed by another command, since any '|' is considered part of the command.

Fortunately we can get around this by embedding that first :norm command in an execute call (:h :exe)...
:g/bob/ exe "norm! A}" | norm! I{

That does the trick. Using :exe allows us to implicitly signal the end of the first :norm.
Note that this is a generally applicable solution that answers the question "How do I follow :norm with another command?".
Comment: If it is used in place (not inside a script) i would prefer to insert a literal Escape: g/bob/norm! A}I{
Comment: @SaulAxelMartinezOrtiz If you're talking about those times that one enters a command manually I would tend to use Ctrl-V myself. In any other scenario, including when providing answers here, I avoid Ctrl-V. Such commands are very often ambiguous to folks who aren't familiar so extra explanatory text is necessary. And they frequently cause trouble for people who unknowingly try to copy/paste such commands.


What tags relate specifically to professional restaurant issues?

Question: Most questions are about gastronomy and food safety. I see 22 pages of tags. Are any intended specifically for food industry?
Answer: Until now, we have not seen the need to make a difference between questions for food industry and for home cooks. Our audience is mostly home cooks, but we have some professional chefs posting, and also a few questions which are obviously intended for commercial food processing. They generally get the same tags as the other ones. After all, a thickener is a thickener no matter if you are going to serve your jam to your family, to guests in a restaurant, or to ship the cans to a supermarket.
But our tags are user-created. Users with a certain amount of reputation can create new tags, and if you don't have enough reputation, you can flag your own question for mod attention and ask a tag to be created if you feel it's needed, for example industrial-processing or whatever fits the question.
If you suggest such a tag, there are different possible outcomes:

The moderator creates it for you, it gets used and gets established. It still won't guarantee you completeness, because users might not think of using it even when it is appropriate. But it will make it easier for you to find industry-applicable questions if that's what you need.
The moderator doesn't create it for you, because he judges that your proposal is not a good tag. See for example this description of which tags are bad. Whether it gets approved or not will depend on the specific tag you propose and the usage you have in mind for it, but there are no long-term consequences for you as a user to suggest a tag which doesn't get approved, so it doesn't cost you much to try.
The moderator creates it, but other users don't apply it to their questions. The system here has automatic cleanup and deletes unused tags after some time (I think it was 6 months).

Note that we have tags about questions here. That's it. We don't have categories of questions with subcategories; we don't have categories of tags. We don't say that "these tags are for industry only, the others are for home cooks only". Even if this separation was possible, such a strict categorization with rigid ontology is frequently counterproductive for information discovery even when properly applied (and it becomes almost impossible to apply properly by laymen). But in this case, it is not even possible. Take the food safety - it is a big topic in industry, but frankly, most of the questions we get here for this tag are from home cooks who forgot a piece of meat on the counter overnight and are looking for somebody to tell them what they want to hear but already suspect is untrue (that it is not officially safe to eat it).
Comment: Thanks for your thoughtful response. My question relates only to hot holding for restaurant service overcooking vegetables--because broccoli still has to be maintained at +140F (hot foods hot sort of thing). I was thinking to ask the community, but its such a specifically food industry question... I didn't think there were food industry only tags, only that someone might speak up about food industry tags that exist here. Then I could read some Qs and determine for myself if my question has _any_ interested parties. Peeps subscribed to tags. etc.
Comment: @xitan it is always nice to see users who take into account the suitability of their questions to the site audience :) In your case, I understand that such a tag would have been useful, however, it doesn't exist yet. You can ask your question, and then I can create something like [tag:restaurant-practices] for you, or maybe some other wording. I think that the question you mention will be received positively on the site, even though I am not sure that we will be able to tell you any tricks you don't already know. But it is worth trying.
Comment: The only "trick" I know is to use batch cooking. The other way to approach this question is to look for recipes which stand up to this kind of hot holding. You see I'm thinking I've succumbed to [information bias](http://en.wikipedia.org/wiki/Information_bias_%28psychology%29), and I already have my answer--as you suggest.
Comment: Only one other idea comes to mind, but its really an argument. Why should cooked vegetables (hot food) need to be held hot when raw fruit, such as apples, bananas, and the like are not kept cold but at room temperature?


How to deal with a stubborn sysadmin?

Question: What do you do when a sysadmin is set in his ways, even though you can prove that the solution's he's using are potential hazards to security/integrity? Or in a case where your sysadmin is supposedly "senior" but makes rookie mistakes on a regular basis? (and then complains that noone else should be doing sysadmin work when you try and fix the issues!)
Comment: This should be a community wiki, I think
Answer: Without going into detail, this is definitely an issue to take to management if it can't be addressed effectively with the individual in question. I would try to engage the other person and give him the opportunity to explain his rationale', however, given the arrogance and ego often found in our industry, it wouldn't surprise me if he didn't appreciate such challenges to his "authoritay."
At that point, you should build a solid logical, financial, and pragmatic case to counter his broken practices and you should suggest a few alternatives (NB: complaining without suggesting solutions is called 'whining'.) At the very minimum, get a copy of "The Practice of System and Network Administration" and start looking for best practices. Put your concerns down in writing. Each organization has different attitudes toward 'argument from authority' (e.g. do textbook best-practices trump those from the local sysadmin or management or developers or Marketing?) If possible, leave a way for the senior admin to 'save face' to make it easier for them to change, without necessarily admitting they were wrong.)
I wouldn't worry so much about not 'being on the team'; it's one thing to be a destructive, disruptive or obstructionist element; it's quite another to make change a positive experience for everyone involved. That said, depending on how dysfunctional your organization is, your choices may be to change your job or change your job - either fix it or find someplace else less broken. That's probably an extreme case though; keep it depersonalized and positive, listen more than you speak, and above all keep a paper trail. :)
Answer: That's hard to determine.
In my experience, you need a champion (direct supervisor) to be aware of this situation, and understand the implication of not being "on the team".
Once you have a little backing, you can be a little more confident that your observations on security should be handed down to the sysadmin, and that conforming with policy should be more strictly adhered to.
Maybe instead of fixing the issues yourself, getting involved in "helping" fix the issues is the way to go.
Answer: I guess that depends on who you are asking... If the question is meant for a fellow sysadmin, then in my opinion, whatever the "rank" (senior, junior), sysadmins should help each other in fixing problems instead of making it a race, a competition or something like that. After all, you are working in the same workplace, you have common goal of keeping your company's infrastructure in working condition, what's the sense in fights, disagreements? As for the mistakes - everyone can have a bad day, just point the error and help fixing it.
Comment: Well said.  When you combine strengths you have a great team, when you let the team fall apart you've got a lot of extra work ahead of you.
Answer: This is a political issue, rather than a technical one. As has been mentioned several times already (because it's a good idea) going to management with your concerns is a perfectly valid way to address the problem. If that avenue is blocked for some reason, you're left with peer pressure. This becomes even more problematic if said admin is already seen as very senior and thus has a lot of clout. In that case you may not be able to do anything about it.
Document what you DO find. If it turns out their careless attitude gets them into hot water, having supporting documentation on hand can help reduce their clout with management and peers, which will in turn make it easier on you to convince others that you may know what you're talking about. That's a delicate line to walk, but if you're not willing to get another job because of this it can work out.
Answer: Inform your manager that you disagree with this and here's why and the risks associated with that.  Keep hard copies of what was sent just in case it becomes necessary to defend that you brought up this concern and it was discarded.  This also assumes the sysadmin isn't in your line to the executive where you are.
You could also ask the sysadmin why he does things a certain way as perhaps what you see as a rookie mistake is actually sensible for some other reasons that you don't know.
Those would be my suggestions along with noting that if you seem to meet a lot of resistance, you may just become apathetic to the whole thing.
Answer: If you work with others at the same level, band together with them against this individual. Not in a confrontational way, but in a supportive way. Such as, have someone propose the same fix as you if you have proposed it to him and he refused. If multiple people give the same idea, he might take it.
If you are alone, go to your immediate supervisor, or, if he is in that position, the next person above. Do your best to bring your concerns out, but not accuse him of being an idiot outright.
Comment: I've used exactly this method to work around a certain project manager (not this job). It works.
Comment: There's a concept called 'delegating up' and it's one of the values of having a manager. Some decisions are not in your power to make or implement so it's perfectly appropriate to raise a concern to your manager, make a few suggestions, and leave it to them to decide how to proceed. You've done your part to inform them of an issue and since they make the big bucks (heh), they're paid to make the hard decisions. It may not fall out in your favor for whatever reason, but you've done about all you can do without being a bastard.
Answer: Maybe you need to find out why their doing something that way first, rather than just trying to "prove" them wrong.  It may be that there is some service that requires a dropping of security.
It's always easy to suggest "improvements" if you're not resposible for a system - but I find one of the biggest factors to stability is unnecessary change, and the more changes people want the less stable a system become.
Then theres always the case of "I'll do it" - someone who isn't responsible for a system suggests an improvement that they will look after, then they leave and the sysadmin has to pick it up.
Maybe I'm your sysadmin?
Answer: At first I'd think, perhaps it is me who is misinformed and wrong?
Comment: Sometimes business need trumps security, esp in smaller networks.  It's possible to let an ivory tower vision of The Perfect Network interfere with doing the job well.
Comment: You are, of course, correct. While not networking related, I can easily give a following example: should all developers be allowed to log in with administrative privileges or not? Having everyone work as a "plain" user certainly improves security, but, on the other hand, the business does suffer. So yes, one must compromise.
Answer: Start documenting.
The scenario you stated could be extrapolated to any other industry; accounting, agriculture, automotive (just to pick three from the same letter in the alphabet). If your documentation is consistent across a large portion of time (not just the stuff that he is mucking up) then it's more likely to be taken at face value.
Good luck.
Answer: It depends on your local employment laws but I'd start interviewing for a replacement.
If you're lucky it might 'motivate' the existing sysadmin.

How to deal with a stubborn sysadmin?