What does it expression tells us when we write Shannon entropy in terms of continues distribution?

Question: Shannon information is defines as,
\begin{equation} H(p_1, p_2,...p_n) = - \sum_{i=1}^{N} p_i log p_i.\end{equation}
For continues distribution, we can write shanon information as,
\begin{equation}H(x) = \int^{\infty}_{-\infty} p(x) log p(x).\end{equation}
For equation one, it is for discrete case. It is showing shanon entropy for set of N outcomes. I want to ask that for continues distribution, we are taking integration limit to infity. what does it means does it means that we are considering infinite number of events? can we take integration from 0 to 1 or 0 to 2?
Comment: related: https://physics.stackexchange.com/q/658980/58382
Answer: For continuous probability distributions, we have what is called differential entropy. For a continuous random variable X with probability density function p(x) defined on the interval I, the entropy is given by the expression as you have given,
$$H(X) = -\int_{I}p(x)log(p(x))dx$$
For example, Let's say we have a normal probability distribution given by,
$$p(x) = \frac{1}{\sqrt{2\pi}}e^{-\frac{x^2}{2}}$$
This function has a non-zero value everywhere in the interval I = ($-\infty,\infty$) and tends to zero at infinity and hence the limits of integration. Looks something like this,

Source
Comment: However, on differential entropy, see, for example: https://stats.stackexchange.com/questions/50246, https://stats.stackexchange.com/questions/256203/how-to-interpret-differential-entropy
Answer: Discrete and Continuous probability distributions
Note a discrete random variable https://en.wikipedia.org/wiki/Random_variable $X$ takes on discrete values say for example in $\mathbb{N}$ with positive probability. Discrete random variables can be described by their probability mass function $p$. These describe experiments like dice rolling etc.
Continuous random variables are described by their probability density functions, and give distributions like the height of a population etc.
Entropy
From an information theory point of view we can ask how much information we receive when we observe a specific value for a random variable $X$, if we are told a highly improbable event has just occurred we will receive more information than if we are told a very likely event has just occurred ( make sure you understand this sentance because it is at the heart of the description of entropy, this link will help : https://www.quora.com/Why-does-an-unlikely-event-give-us-more-information-than-a-likely-event#:~:text=The%20higher%20the%20probability%20of,previous%20beliefs%20will%20be%20disrupted. )
$\underline{\textbf{Constructing a function that measures the information content :}}$
Lets call this function $h(\cdot)$.
Our measure of information content will be a monotonically increasing function of the probability mass function $p(x)$. Construction of such a function can be motivated by the following observation, that is, if we have two events that are unrelated then the information we gain from being both of them occur should be the same as the sum of the information that each of them occur separately :
$$h(x+y)=h(x)+h(y).$$
Note two unrelated events will be independent, i.e
$$p(x,y)=p(x)p(y).$$
Using these two facts, one can show that $h$ must be given by the logarithm of $p$, so that
$$h(x)=-\log p(x)$$

Here we can (arbitrarily) choose to use the natural log, which has many nice links to physics. In information theory the convention is to use base two, whereby the units of $h(x)$ are 'bits'.
The negative sign ensures the entropy is positive or zero.

$\underline{\textbf{The entropy of a random variable : }}$
The average amount of information it would take for a sender to transmit value of a random variable to a receiver would then be the average of $h$ with respect to the probability distribution $p$ https://en.wikipedia.org/wiki/Expected_value, i.e :
$$ E[p]=-\sum_{x}p(x)\log(p(x)).~~~~~~(1) $$
This is called the entropy of the random variable $X$. I like to think of it as a $\textit{functional on the space of probability measures }$. Note the reason it is a sum is because we have assumed $p$ is a mass function associated to a discrete random variable. Then a natural way to extend the definition of entropy to continuous random variables is to define it as the expectation of $\log(p(X))$ for a continuous random variable $X$ giving
$$ E[p]=-\int p(x)\log p(x).~~~~~~(2) $$
To be properly defined note that in $(1)$ as a functional the entropy is defined as a map acting on the space of probability measures over some discrete set whereas in $(2)$ it is defined over probability measures on a continuous set - Infact in $(2)$ we have assumed that the measure of $X$ admits a density which we have called $p$.
Your question : $"\textbf{can we take the integration from 0 to 1 ?}$" Answer - no you must integrate over the support of the distribution of your random variable, by the above construction it would not make sense to do otherwise.
There is a more in-depth discussion of entropy from a information theory and statistical mechanic point of views in the book "Pattern Recognition and
Machine Learning" of Bishop - as well as a detailed description of going from the discrete to the continuum.


php file_get_contents causes segmentation fault (11)

Question: I'm having a problem where the php function file_get_contents causes segmentation fault (11) error.
This problem started when many of my php scripts suddenly started causing browser errors like "ERR_EMPTY_RESPONSE", etc. So i tried finding out what all those files had in common. And then found out that loads json data from external servers via the file_get_contents function. I tried removing that function from one of the files. And sure enough. The script suddenly works (but not loading the data. Obviously.) All of these scripts loads content from different urls from different servers from different companies. So i already know that it's not any specific url or file.
Here's a sample from my apache error log:
<code>[Thu Jul 30 16:43:58.890237 2015] [core:notice] [pid 2833] AH00052: child pid 4729 exit signal Segmentation fault (11)
</code>
I've been searching around for hours. Trying to find solutions, workarounds, alternative functions, etc. But with no luck. The only solution i found was to change php mode to "fast-cgi". Which i don't want after reading that fastcgi will not let me serve page rules via .htaccess anymore. (Half of my sites runs of rules defined in .htaccess files).
Does anyone have any idea why this is happening? And how to fix it? I may also note down that i never did anything to cause this. I never changed anything in any configurations or anything. It simply just started happening a couple of days ago. So there must be some way to fix this error right? Thanks in advance!
Answer: Try using an other method to get the file content. As suggested by a user here who seems to have the same problem:
http://kb.odin.com/en/125759
<code>function get_content($URL){
   $ch = curl_init();
   curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
   curl_setopt($ch, CURLOPT_URL, $URL);
   $data = curl_exec($ch);
   curl_close($ch);
   return $data;
}

$filecontent = get_content("URL");
</code>


Cranberries on Passover

Question: Are fresh cranberries, bagged with OU (year-round) certification, kosher for Passover?
Answer: According to the cRc site:
"Cranberries - Fresh do not require kosher certification. Dried require a reliable kosher certification. "
The Star-K says that fresh produce bought in a supermarket poses no problem.
Chabad.org writes, "Fresh, unprocessed fruits and vegetables, however, do not require certification. "
Page 92 of the OU Passover guide (from 2013) says that frozen fruit needs no certification ("However, these issues are not a concern at facilities that process frozen fruit, which does not require Passover certification.
"), so I would guess that they would agree that, all the more so, fresh fruit doesn't.
Comment: @msh210 regardless, why would a fresh vegetable require any certification? (***note***: this is not the same thing as *checking* produce, which is still necessary.) Bagged, certified lettuce exists basically to save people the trouble of checking.
Comment: The cRc (sic, not CRC) page you link to is not discussing Passover afaict.
Comment: @msh210 thanks for the clarification. I read through their pesach list and they don't mention any concern with fresh cranberries (unlike raspberries, blueberries and blackberries).
Comment: Typically frozen veggies are processed on the same lines that make pasta, this would be an issue obviously. This isn't 100% so you'd want to check accordingly.
Comment: @IsaacKotlocky But the citation in this post is incorrect. The answerer implies the cRc is referring to _Pesach_. You wanna argue fresh berries don't need KFP certification, I won't be on the other side of that argument -- but don't cite that cRc page as support.

Cranberries on Passover


What kind of connector do I use for the Pi's GPIO pins?

Question: Does the Raspberry Pi have its own connectors for the 26 GPIO pins? If not what connectors do Pi users typically use for connecting these pins to peripherals?
Answer: You have a couple of options:

Female to male jumper wires (for use with a breadboard),
Alternatively you can add a set of female headers to the Pi and use the more common male to male jumper wires,
You can use a floppy drive ribbon cable (because the cable has more pins than the Pi it will hang over the edge and prevent it from being used with a case/enclosure),
You can make your own ribbon cable,
Adafruit (and most other Pi suppliers) has a ribbon cable (also available in white though not linked) specifically made to fit the Pi that works with many of the available cases.
They also offer a product called the Pi Cobbler which includes a cable, PCB and headers which make protoyping with a breadboard a breeze (this too is available in two styles)

For a more permanent installation I might use a ribbon cable and etch a custom PCB.
In the end which method you choose comes down to price, convenience, and how much you will be modifying your circuit.
Answer: The pins are standard 0.1 inch spacing pins, so you have a lot of options including

ribbon cable with IDC connectors. Good option if you want to bring all the pins to another board using a single cable. Downside is that the IDC connectors have wide sides which means you must use one that completely covers the header.
single pin crimp sockets. These are commonly found on jumper wires and often used for prototyping. Not a great soloution for final systems though as connecting and disconnecting the Pi is a pain.
crimp pins in larger housings. These are readilly available from large electronics suppliers but the crimp tools can be a bit pricy. You can also sometimes salvage them with wires always attatched from scrap PC cases. These can be a good soloution if you want to connect to a group of pins but not the whole header or if you need wires going off from the header to a variety of places.
various styles of board to board connector including ones with long square pins that allow stacking.

Unfortunately every brand has it's own names for these things, so finding them in supplier catalogues can be a bit tricky.
Answer: The connector types you may be looking for are called dupont connectors and have a pitch of 2.54mm. Searching for "dupont connector kits" should yield good results.
Otherwise, rectangular connectors can be found on the common electronics supply sites, such as Digi-Key or Mouser. You'd need to pull up rectangular connectors and narrow it down to the ones that have 2.54mm pitch.
Comment: This adds nothing to the accepted answer.


What happens to canceled requests to a PHP page?

Question: When a long-running PHP file is executing, and the user cancels the page request in their browser midway, is the rest of the script ran on the server?
Comment: AFAIK, they will still complete execution on the server. Why don't you test it out? All you need to do is place some sleep in your PHP file.
Comment: Haha, I was just looking at the PHP sleep function on php.net when you said that.
Comment: I'm with @AlecSmart. If you've ever accidentally sent a massively unoptimized database query via phpmyadmin you know the process can run for a lonnnng time after you've developed blisters clicking the stop button. This may be a result of the MySQL server being involved though and you could get different results from a purely PHP script with no db access.
Answer: PHP normally terminates script execution once it realizes that the connection is closed:

PHP will not detect that the user has aborted the connection until an
  attempt is made to send information to the client. Simply using an
  echo statement does not guarantee that information is sent, see
  flush().

You can keep your script running using ignore_user_abort().
Also, there is a default time limit for which scripts are allowed to run.  You may want to override that using set_time_limit().
Comment: Use transactions when appropriate, that's what they are for.  Your script may terminate early regardless... power outage, server crash, etc.
Comment: Using register_shutdown_function() with a connection_aborted() test can allow you to put in special handling for a trapped user abort, letting you clean things up before script execution actually terminates... though it does have some limits. Database transactions should be used to handle rolling back all db activity in an aborted transaction - transactions were invented for precisely this purpose long before PHP or the web ever existed.
Comment: Terminating the script execution sounds... insecure. Especially when making MySQL queries.
Comment: Excellent point. I'll have to start doing some looking into transactions.
Answer: I tested this once on a long running process and discovered that the script will continue to run once it has not exceeded the maximum time to execute.
Answer: For me (using XAMPP on an older computer), cancelling the web page in the middle of an operation meant to process one million primary records, with a couple of other tables being updated in the process, the MySQL database operations kept going, which tells me that the PHP script kept running on the server.  By "cancelling," I mean clicking the stop button on the tab, but not closing the tab altogether.  BTW: I had established set_time_limit() to 0 to keep the script from timing out before completing in absence of cancelling.


Cant find redeem code on starcraft 2 digital purchase

Question: Can someone help me locating the game key of the Starcraft 2 WOL i just purchased? The only email blizzard sent me was the transaction. No links or whatsoever.. I already installed the starter edition then upgrade it but redirects me to the buy link of starcraft 2. I bought it but dont know where is the redeem key.. Any help?
Comment: check your spam filter
Answer: If you have bought the game directly on Battle.Net, there is no code to be redeemed. The game license just gets directly added to your account, which you can check at https://eu.battle.net/account/management/ (or US site).
You can then download a game client from the site, but if I recall correctly, the Starter Edition should download an update automatically, did it not?
Comment: IIRC there shouldn't be any update needed, game access should change based on which account logged in, so it should usually be enough to logout and log back in after waiting a bit.
Comment: @Mario Right you are. The game is installed completely anyway, so that any user can log in and play his respective game.


Git ghost commit eludes log

Question: Today I was working on one of my projects and I realized some weirdness with git. Git would allow you commit your work to a ghost branch. I use the term ghost branch because the changes exist somewhere in the tree but evades git log --graph --decorate --oneline --all. Can anyone explain to me why this is?
Steps to reproduce this behaviour
Enter detached head state (you can get there by performing git checkout <hash>).
# Not currently on any branch.
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#   uml 1.pdf

Make some changes to your codebase. And check the status of the working directory using git status. This should list the changes but state that you are not on any branch.
# Not currently on any branch.
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#   modified:   .gitignore
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#   uml 1.pdf

Commit the changes using git commit -am '<message>'
[detached HEAD ded7725] updated .gitignore
 1 files changed, 8 insertions(+), 1 deletions(-)

If you then checkout a known branch, "master" for example, all changes commited in the detached head state is gone. This is expected.
Runnig git log --graph --decorate --oneline --all will show all commits except the one committed on the detached head (ded7725 in my case).
However, a git checkout <hash-for-ghost-branch> returns the changes committed to the ghost branch. Problem is: one cannot remember this hash forever.
The expected behaviour would be that this ghost branch will be on log the graph in a somewhat hanging leaf. But it is not present. Any explanations as to why this happens is appreciated. Or maybe I am missing out on a flag to show hidden branches...
Comment: `Problem is: one cannot remember this hash forever.` I suspect that's not the only problem. Have you checked to see that this commit survives `git-gc`? I wouldn't be surprised if it doesn't. Committing to a detached head is not part of any sane git workflow, but nobody ever said git wouldn't help you shoot yourself in the foot...
Comment: @grossvogel shockingly, the ghost commit survived a `git gc`. I don't think the garbage collection deletes unreferenced branches.
Answer: The "ghost" branch, as you call it, is not a branch.  It's commits on the DAG which are not pointed to by anything.
Although I haven't looked at the code, I would imagine git log draws the graph and lists the commits by starting at the branch pointers and working backwards.  Since your commits in a detached HEAD state have nothing pointing to them, there's no way for git log to "see" them.
To fix that, simply create a branch with git branch branch_name <commit>.  Then git log will have something that points to the last commit done in the detached HEAD state and will "find" those commits when displaying the log / drawing the graph.
Answer: The root reason that this "ghost" branch does not appear in your git log --all is that this log will only represent all branches, not all existing commits.
You have to consider that when you rebase commits you do not delete the old commits you just copy them to another parent, so they also are commit without any branch, like your ghost branch.
commits are like objects referenced by other objects, the only objects kept by git are the one referenced by branches. It is really like a garbage collected memory, your commit is an object you created in memory without referencing it. If you run git gc git will delete all these commit not referenced by any branch, including your "ghost branch".
The solution for you is to keep a reference to this commit, either by creating a branch as explained by wasworld, or by tagging your commit git tag tagname sha1.
EDIT: git gc will not delete recent commits, according to its manual page:
The optional configuration variable gc.reflogExpire can be set to indicate how long
historical entries within each branch's reflog should remain available in this
repository. The setting is expressed as a length of time, for example 90 days or 3
months. It defaults to 90 days.

So your ghost branch will be safe from git gc (which can be started without you asking for) for 90 days by default.
Comment: Are you sure `gc` will delete it even if it's still reachable from the reflog?
Answer: In git branches are just pointers to commits. So when you say "Problem is: one cannot remember this hash forever" why not just create a branch at it?
git branch branch_name <commit>

What also is to keep in mind is that if you don't create any branch that points to this commit it will be gc'ed once the expiration time passed by. The default is 90 days.

Git ghost commit eludes log


What extreme measures might a pilot take to avoid extreme weather?

Question: What kind of extreme weather would justify a pilot of a commercial airliner taking avoidance measures to the point of likely stall?
Comment: You are assuming that the events leading to the "point of likely stall" are deliberate and controlled.  In real world cases where this scenario has been a contributory factor, this has not been the case.  No sane pilot is going to deliberately fly into a stall unless training.
Answer: Any which the pilot thinks is more dangerous than the avoidance measures?
If you were driving at 100mph towards a wall which you reckoned had a 90% chance of a head-on collision, or could attempt to turn which had a 50% chance of throwing you off a cliff, which would you choose?
Any decision the pilot makes will be made on the basis of "Taking this action is a better option than not taking it".
The main weather which would likely cause this would be high enough levels of icing to be dangerous, or such severe turbulence that the pilot believes the plane will be "upset" enough to throw it out of the performance envelope. A combination of these may be present in a severe storm.
Comment: Possibly debatable, but not just turbulence.  Severe up and down draughts can overwhelm an aircraft's ability to fly out of them.  I see these as distinct from turbulence.
Comment: Yes I definitely suggest not attempting to fly out of (or into, or through) any mountains
Comment: I see what you mean, in that Turbulence is chaotic whereas an updraught/downdraught system is on a larger scale so appears more "ordered", but both tend to come as part of a storm and are really just a type of turbulence (ie chaotic air movement). Also, attempting to climb out of or over an updraught is somewhat defeating the object.... either way, that seems to me to be arguing semantics, not principles.
Comment: @JonStory a very strong mountain can be very difficult to fly out of, especially in the Q corner.
Comment: Thanks for your answer Jon. I assumed that there must be weather conditions which were so dangerous as to warrant a relatively risky course of action to avoid them.  My interest was in what those conditions might be. A point which you have addressed in your last paragraph. Thanks again.
Comment: Sorry word left off. "Mountain wave"
Comment: That does make a fairly significant difference :) although I maintain that the original answer stands: the pilot will climb where s/he feels that the risk of climbing over a weather condition is lower than the risk of passing through/staying in/going around it it.
Answer: If you are talking about the AirAsia Crash, you may have some misapprehensions.
Normally, the problem with a storm is not "avoidance" once you are in it. The problem is keeping the aircraft flying in a stable configuration in the presence of violent winds. A powerful enough wind can literally turn a small aircraft upside down and backwards. Big Jets are much less susceptible, but can still be thrashed around violently in a storm. The pilot has to react to these upsets and keep flying. So, for example, if the winds put you into a stall, you have to recognize that and do what is necessary to keep air moving over the wings properly. Sometimes, the necessary actions might be completely unintuitive or different than what is normal. For example, if you are upside down, some of the controls work in reverse. If you do not know that, or are not practiced in flying upside down, then making that adjustment can be difficult.
A big problem in such circumstances is that in a storm you may not be able to see the horizon, so you have no visual reference for horizontal stability. Moreover, the artificial horizon, the instrument that tells you your attitude, has a lag, so what you are seeing on the instrument was the situation 1 or 2 seconds ago, whereas your current situation may have changed. In a spin or other rapidly changing flight condition the artificial horizon will be wobbling wildly and unpredictably and is less useful than normal in determining what the true attitude of the aircraft is. In a non-visible conditions this can lead to disorientation.
In the case of the AirAsia flight, the storm could have been putting them into a stall and the aircrew's reactions were not vigorous enough to correct it. Unless details are released on their control inputs and other data, we have no way of knowing. Also, they may have just taken the wrong actions. For example, if you are in normal stall you push the stick forwards to get the nose down, but if you are nose up and upside down, then you have to pull the stick backwards to get the nose down. Since you cannot see, it can be difficult to tell if you are upside down or not.
Also, sometimes a pilot will panic if they are losing altitude fast and pull back on the stick, a fatal reaction. Being inside a storm can be very frightening, even to pilots experienced with flying in them (such as meterological pilots), so panic is a real possibility. Once a person becomes panicked, their training goes right out the window and they can do very illogical things. I was once in aircraft with a high-hour CFI who panicked and he did some crazy things.
Comment: That's news to me. Asked as a question to get more info: http://aviation.stackexchange.com/q/11924/136
Comment: @NathanG Not only does the "AI" lag, it lags by different amounts depending on what you are doing. Lazy turns can cause really long lags. During upsets or gusty conditions it will rock back and forth and be very difficult to use.
Comment: QZ8501 was no Cessna 172 with 40 year old mechanical attitude indicator. It was A320 with AI fed by inertial reference system that can do pretty precise dead-reckoning and is used for flight controls and with alpha-limit that already saved many planes from crashing when they approached stall in heavy turbulence. If they really stalled, which we can't know for sure until NTSC publishes FDR data, there must have been a technical problem in addition to whatever mistake pilots may have made.
Comment: Thanks Tyler. I am not specifically referring to the AirAsia crash but rather am just interested in what kinds of weather conditions might be so unattractive as to make a pilot take extreme and possibly dangerous evasive action prior to entering those conditions. I'm interested because various 'fear of flying' resources reassure nervous fliers that modern passenger planes are built to withstand any weather conditions they are likely to encounter. This appears to be borne out by what you are saying but instead places the focus for crashes firmly on pilot error.
Comment: @Tom Well, first of all, icing can bring down any plane if it is severe enough, so pilot error is not the only factor. You never have to take "extreme" maneuvers to avoid a storm front, you just turn around. A plane can fly a lot faster than a storm. Most crashes involve a pilot making one or more mistakes, however, take into consideration that flying is very complicated, so expecting pilots to make perfect decisions without exception in a crisis is not realistic.
Comment: `"For example, if you are upside down..."` If you are upside down in an airliner, you probably have bigger problems than the stall condition (unless maybe you're [Tex Johnson](https://www.youtube.com/watch?v=Ra_khhzuFlE).)
Comment: Does an AI really have any non-trivial lag? A gyro-based AI would tumble in an upset, and has minor lag from erection, but should otherwise be accurate in real-time. A glass AI should update pretty quickly, without those flaws.
Answer: Realistically I can only think of one: downburst on final approach. In downburst the aircraft in relatively quick succession encounters headwind, downwind and tailwind. The increase of headwind causes increase in airspeed, but loss of kinetic energy due to increased drag. Then the downwind simply causes loss of altitude and finally the change from headwind to tailwind causes loss of airspeed that may be easily large enough to stall the aircraft.
If this dangerous phenomenon is encountered at low altitude (it only occurs at low altitude, too), the pilot must fly the aircraft at the edge of stall to preserve as much height as possible and hope the engines will be able to make up for the lost energy before he runs out of it. It is the reason Airbus introduced alpha-limit on A320 and alpha-protection already earlier. Alpha-limit limits angle of attack to just below stall when the side-stick is moved all the way aft and alpha-protection sets full power when a slightly lower angle of attack threshold is exceeded.
I suppose this is not what you meant. No, I can't think about anything at high altitude that would call for such aggressive manoeuvre. At altitude either you see the weather developing ahead for couple of minutes (with eyes or on weather radar) and avoid it using normal manoeuvres or you hit unexpected clear air turbulence and just react to it. And clear air turbulence is quite likely to make the plane loose altitude, hundreds of feet, rarely even couple thousand feet, but not gain it.
Comment: Relevant reading, perhaps, for those interested: https://en.wikipedia.org/wiki/Delta_Air_Lines_Flight_191
Comment: _"And clear air turbulence is quite likely to make the plane loose altitude, even couple thousand feet, but not gain it."_ Unless it confuses the alpha protection, which then [sends the plane into a steep, uncommanded climb](http://www.aaib.gov.uk/cms_resources.cfm?file=/Airbus%20A330,%20C-GCWD%20Airbus%20A340,%20TC-JDN%2006-2001.pdf).
Comment: "Even couple thousand feet" - excessive, surely? I've never heard of clear air turbulence causing more than a couple of *hundred* feet of altitude loss. A microburst can cause more of a drop, but that's not clear air tubulence
Comment: @JonStory: Usually hundreds, but thousands seem to happen occasionally. In [this incident](http://avherald.com/h?article=479df3b9) it was 7500 ft. That would include altitude lost while recovering from any attitude the turbulence got them in.
Comment: Tailwinds causing a loss of  indicated airspeed is a myth
Comment: @rbp: So what happens when the headwind changes to tailwind as you pass through a downburst according to you (I never claimed anything about tailwind in general, only in context of downburst; I'll try to make it more clear that I don't)?
Comment: you're confusing updrafts (plane speeds up at same altitude/power) and downdrafts (plane slows down at same altitude/power) with head/tail wind http://en.wikipedia.org/wiki/Microburst#Danger_to_aircraft


Who will be my final adivsor?

Question: I am presently a third year graduate student. I am currently being supervised by professor A. Recently, I am co-supervised by professor A and B. Now professor A decides to leave, and if I graduate in two years, who will be my final advisor? A or B or A and B?
Comment: What do A and B say concerning the matter?
Comment: Why *wouldn't* you discuss it with your advisor?
Comment: Voting to close because only A and B can answer it, as they are the ones who truly know your case.
Comment: I have not discussed that. Should I discuss it with A and finalize now itself? Can A be my final co-advisor, even if he leaves the university?
Comment: I can, and that would be the right thing to do, right?
Answer: I've been in this situation as Professor A. One student moved with me to location U. One stayed a student of location K but spent a lot of time in location U. The other stayed in location K. I still supervised him, but he worked a lot more extensively with Professor B.
U and K are in different countries, but K kept me on in a 10% appointment so that this would work administratively.
I told the students I was leaving and gave them all possible options I could cater for – unfortunately, I could only pay for one of them at location U. For various reasons, students took an option that suited them.
Before you discuss it with Professor A, you need to think about what you want, assuming that following Professor A is an option. And think about how well you would work with Professor B, if you cannot follow Professor A. The last thing you want to do is be left without adequate supervision.

Who will be my final adivsor?


Is it possible to create BTRFS snapshot for a directory?

Question: When I tried to create a snapshot:
[root@localhost ~]# btrfs subvolume snapshot /home/admin2/ /.snapshots/s2
ERROR: Not a Btrfs subvolume: Invalid argument

How to create BTRFS snapshot for a directory?
Answer: No simple way is known to me. I would say no, it's not possible directly.
If admin2/ was a subvolume then there would be no problem. I don't think you can transparently and instantly convert a directory to a subvolume though.
There's a workaround:

Create a snapshot of the entire subvolume that holds admin2/.

Remove everything but admin2/* from the snapshot.

Rearrange data in the snapshot:

move the content of admin2/* to the top-level directory of the snapshot;
remove leftovers (e.g. admin2/* directory, now empty) from the snapshot.

Change ownership and mode of the top-level directory of the snapshot according to the original admin2/ directory.

This way you manually create a subvolume that is what you want: a snapshot of a directory.
If you think you'll want to repeat this process in the future then consider replacing the original directory with the subvolume. Move the directory out of the way (rename or remove it), then move the subvolume into its place. Note the subvolume becomes /home/admin2/ so you will most likely want to create yet another snapshot. But now creating a snapshot is easy, the command you tried should now work.

* Do not confuse admin2/ in the snapshot with the original directory. Where I denote admin2/ with asterisk I mean admin2/ in the snapshot.

Meta note: Frankly I almost duplicated this other answer. The question there is about converting a directory into a subvolume, something you may or may not want to do. Because of this one difference I didn't simply point you to the other answer; I decided to explain the procedure in context of your question. But the difference is mostly in the question. The only difference in the procedure is whether you eventually change few names or not. If you find my answer useful then consider upvoting the linked one.
Answer: Snapshots can only be taken for subvolumes. There is no direct way to convert a directory into a subvolume.
But if you only want a copy of the directory sharing the same data on disk, you can follow the BTRFS Wiki and use cp --reflink:
cp -ax --reflink=always src/. dest

This will create just a normal copy of your directory but instead of copying all the file data it will be shared (=reflinked) with the original directory. Basically this is the same as a snapshot and if you want to have the copy in a separate subvolume you can just create an empty subvolume and copy the directory into it.
Depending on your data this may be faster than @Kamils answer because deleting all other files may take while for a huge number of files.


camera mobile phone takes pictures at constant focal length if 3.5 mm.supposed to have autofocus and touchfocus

Question: This is a cheap Chinese landvo l200
Android mtk65xx mobile
The onlything it keeps
Changing is IS0 from 150 to 800 +
And exposure time
I wondered how can it autofocus and touch
Focus when it keeps focal length constant
@ 3.5mm.
Is that the case with all phones ?
Or maybe some high end ones like xperia
And HTC have something more in the camera lens
Answer:
how can it autofocus and touch Focus when it keeps focal length constant @ 3.5mm.

Because focussing is not about changing the focal length. Changing the focal length is called zooming, which your phone-cam doesn't do. Not optically anyway.
Focussing involves changing the distance between (parts of) the lens and the sensor.


How do I handle the existing screws when replacing flashing on a metal roof?

Question: Just had our on-demand water heater replaced. A few days later, I noticed rain leaking around the vent pipe in the attic. The vent pipe has flashing installed on the metal roof, similar to the pic below. It looks like there's a small tear where it seals to the pipe and in general just looks like it's deteriorated a bit. I'd like to replace it with a similar flashing but I'm not sure how to handle all of the screws that were installed around the existing flashing. If I back those out, what must I do to ensure no leaking around them when they are removed? How do I make sure I don't reuse a hole by accident or insert a new screw too close to an existing hole and cause a tear in the metal roof?
Comment: Maybe include a pic of the existing install. Someone might see a better way of fixing it that won't involve new holes...
Comment: I'm not sure I could screw through the new flashing and hit every existing screw hole.
Comment: Why not plan on reusing _all_ the holes in the metal roof instead of making a whole new set of them?
Answer: Hopefully the last guy used #10 roofing screws. Use #12 roofing screws for your installation. Butyl tape makes a nice gasket material instead of (or in addition to) sealant. Leave an unsealed couple inches at the low point so that any water that infiltrates can drain.
Answer: You need screws with neoprene washers.

If you need to make new holes, put one of these screws in the old holes too, to seal them up. Additionally, I'd consider some Henry's, which does come in white too, but maybe under a different name. Replace the flashing and parts as needed, fill all old holes with a screw and washer, then put a generous coat of Henry's on the whole area.
Comment: Ok, that makes sense. So new screws in the existing holes, sealant over them, then replace the flashing.
Comment: @gnomer No, replace flashing first. 1) Get all the new parts into place, 2) screw them down, 3) apply sealant.
Comment: I'm not a big fan of the "generous coat of goo" approach. It looks like poo and can obscure actual problems. Seal the old holes. Install. Seal the new holes.
Comment: @isherwood Except the OP says it is leaking... I turn to the goo when it's leaking. I've wasted too many hours on roofs with a leak, moving this, shifting that, when these days I just slap some goo around the flashing. Yeah, you *see* it, but really only when you're looking for it. You'll forget it's there and probably never see it again. Unless it really stands out, which can be the case on occasion.


Is it safe to delete replication relay-bin files?

Question: I've got a small database, around 50mb. It's a master replicating to a remote server. I noticed that the relay-bin files total to over 5GB. Is it safe to delete them?
Answer: I think a better answer is relay logs can be 'deleted' but mysql should manage it automatically.
One way to do this is to check for the value of relay_log_purge.
It should be set to 1 if you want mysql to manage them:
set global relay_log_purge=1;

You would probably need to flush the logs:
flush logs;

This does not affect the binary logs.
Comment: This should be the accepted answer IMO. We just found a server that had apparently had relay_log_purge turned off manually several months ago and had been steadily filling up its disk with relay logs. Running these commands worked perfectly.
Answer: Maybe try to resync your master and slave.
If possible, cleanup the slave by running a
reset slave
it will purge all relay binary logs.
Then set the replication again with change master to ...
You may have too much lag between your master and slave.
Comment: Worked where the other suggestions didn't
Answer: From the MySQL manual:

The SQL thread automatically deletes each relay log file after it has
  executed all events in the file and no longer needs it. There is no
  explicit mechanism for deleting relay logs because the SQL thread
  takes care of doing so. However, FLUSH LOGS rotates relay logs, which
  influences when the SQL thread deletes them.
Answer: No, do not delete the relay-bin files manually. What you can do is to purge the binary files using MySQL commands. See the MySQL 5.0 Manual for more on the PURGE BINARY LOGS command.
Comment: "PURGE BINARY LOGS" only related to binary logs, not relay logs
Comment: Can these files be deleted if replication has been turned off and won't be used again?
Comment: This does something different as it wask asked, that might harm your mariadb setup. The proper answer is Rodo's.
Comment: Thanks, that's what i needed? Will purge ensure that replication is not affected?
Comment: Yes, replication will not be affected at any time.


Can subject and verb come after the rest of the sentence?

Question: At times, during commentary, commentators speak sentences like "Playing well, Victor is", "A great player, Steven was".
Comment: 'A great player, Steven was.' is in the CompSV form, with an added comma to show where one would pause in speaking. 'Playing well, Victor is.' splits and re-orders the verb phrase. It is more informal, and better avoided in formal writing.
Comment: OK, thanks! Any suggestion on punctuation I used there?
Comment: The jurisdictional question is Which part has been moved? Has the `subj + aux` been moved to the end, or has the predicate phrase been moved to the front? Also, since this is **spoken** English, there are no punctuation standards; do what you think best.
Comment: This is spoken _British_ English.
Comment: This is Yoda Speak. There are online generators that will convert any regular sentence for you. ("Yoda speak, this is. Convert any regular sentence for you, there are online generators that will.  Hmmmmmm.")
Answer: It's grammatical but it's "marked", meaning that this word order isn't the normal declarative order but is chosen intentionally to create emphasis. Even then, it isn't usual, and I'm surprised by your implication that commentators are using it frequently. However, sometimes this order is used for humorous effect, as it reflects the sentence construction of the character Yoda in the Star Wars movies.
Your punctuation is correct.
Comment: Difficult to consider without Yoda, this is.


Can I retrieve sound from laptop speakers that has been cancelled unintentionally while recording from a microphone?

Question: Is it possible to retrieve any sound from laptop speakers which has been cancelled unintentionally while recording from a microphone in Windows 7? I left the option to remove speakers' "background noise" checked by mistake. It seems to me that it is not possible but I would like to have a second opinion. Thank you.
Answer: No. The summing/cancellation/noise reduction was done before the source went to 'tape'. The is no 'pre-cleaning' or diff file to go back to. Most 'smart' or AI processes are designed to remove noise not add, so there is no specialist suite of tools to aid you in reversing this process.
There is the vague hope that there may be some small remnant of this signal which may be boosted after the fact, as a separate file. Some noise-reduction software will let you flip to hear what is being removed, as opposed to the result of removal. There may be some small mileage in taking this & seeing what you can gain from it.
Comment: There are tiny remnants of the original sound removed but most of it sounds like someone is playing an annoying flute. Can you elaborate on how to try to get something from this? I just tried to use a very high level of amplification to be able to hear something. My knowledge is very limited on this.
Comment: It's going to be tough. You're going to have to start with something like Izotope RX [there's a free trial] & go through each of the 'restoration' plugins, noise removers, vocal 'rescuers' & see which has an 'inverse' button, because you're trying to rescue what these plugins are all designed to throw away. It's not like you're starting with a bathtub full of floating toy ducks, trying to fish out the ducks; you're trying to analyse the bathwater… after the bath has been emptied.


Data for site specific path analyzer map is not getting reflected

Question: I have created a site specific path analyzer map. But, unfortunately. I am not able to get the data displayed for the same even after 24 hours. In addition to that , I wanted to know how to link the funnel with a site specific map.
Comment: Is the visitor's data getting captured/tracked properly in your sitecore instance ? Are you able to see the tracked data in Sitecore Analytics ? If not, before checking my answer - you should consider looking at the logs for any exceptions related to xDB etc.
Answer: After opening Path Analyzer from Sitecore LaunchPad, I used to choose All Visits in the site map dropdown menu and then choose the Vertical representation as shown below to see the map diagram with paths and nodes,

If you just want to view a funnel from a site map, check this official Sitecore docs link here
Or if you want to link a custom funnel you've created under Marketing control Panel, then see the below steps :
Step 1 : Go to <code>/sitecore/system/Marketing Control Panel/Funnels</code> and then create a funnel item (by giving some item name) under the Funnels node.
Step 2 : Select the funnel item you just created, and scroll down to the field called Sequence. In this field, click edit and then choose the pages in a sequence that you want to track. Funnels help you understand how many users are dropping off along each pages you've selected in this path sequence before they realize a business objective. For example, we create funnels with paths defined from Home page to Cart page to understand where visitors are bouncing off.

Step 3 : Click the Review tab in the Sitecore Ribbon area and then click the Deploy button, present in the Workflow group.
EDIT: To view the custom funnel
Click Funnels at the Map overview Panel found at the right side of the map as shown below. In the dropdown, choose the funnel you created with the sequence. Then click "Set as filter".

Now, click Apply

You can now see the path for the Lead form funnel (in screenshot) that we created as below,
Comment: Added how to view the custom funnel in the map in the EDIT section


Deleting duplicate cells from notebook

Question: I need to delete all duplicate cells in my notebook, keeping just one occurrence of each pair (or tuple). No need to choose which to keep.
Is there a (simple) way to do it?
Comment: Are they exact duplicates by the structure (Ctrl+Shit+E)? How did it happen?
Comment: I'm not sure I understand your question. If the cells are "duplicates" of eachother, why do you need to choose which one you keep? You could realize this by importing the notebook as "notebook expression" and do a simple expression replacement.
Comment: @halirutan The notebook has a lot of cells (10000+). Some (few hundreds) have one or two duplicate (just some of them). I cannot do the replacement by hand as they are too many. I need to preserve just one single copy of each. Is there a hack to do it programmatically? I mean, how could I scan the cells and keep track of duplicates?
Answer: You may use the Low-Level Notebook Programming guide.
Create a notebook with CreateDocument for the example that has duplicate cells.
SeedRandom[123];
nb = CreateDocument[Table[ExpressionCell[n, "Input"], {n, RandomInteger[{1, 5}, 20]}]]

The Cells can be GatherBy'ed their NotebookRead representation.  They will have different CellChangeTimes so this is made to be the same for all cells.  The first of each gathered sublist is kept and the Rest are NotebookDelete'ed from the notebook.
NotebookDelete@
 Flatten[Rest /@
   GatherBy[Cells[nb],
    NotebookRead[#] /. {HoldPattern[CellChangeTimes -> _] -> Nothing} &]
  ]

The duplicate cells are now deleted.  For the cases where there are no duplicates then they will form a sublist with a single cell.  This cell will be removed by Rest so that it is not deleted.
If running this in the notebook you want to clean-up then replace Cells[nb] with Cells[] to get the cells in the current notebook.
The cells have to be identical in their NotebookRead form for this to work.
Hope this helps.

Deleting duplicate cells from notebook


SharePoint 2013 : Ways to check user activities

Question: I understand SharePoint 2013, unlike the previous versions, have been removed lots of statistic reports. My only requirement is to track everyday which users have login to SharePoint or not. Is there any way to track without access the back end (e.g. check IIS raw log)?
Answer: I do not know of anyway to look only at if a user logged in or not. What you can do is go to the site settings, site collection administration, and then audit log reports. I would run a custom report or a content viewing report depending on the version of SP (online or hosted). Online SP does not support content viewing auditing but you could get a decent feel for how active your users are by including Opening or Downloading and Searching Site Content.
Hope that helps!
Comment: I have considered this approach but we have to setup audit for each site and not for entire farm. We have more than a hundred sites so it is not very nice to our situation.


Can I get a summer job in the US if I study abroad?

Question: I'm a US citizen but I'm doing my Bachelor's abroad. I will be going back to the US in the summer and I wanted to get a summer job but I am not sure how to apply since I live abroad and applications are all for people who live in the US
Can someone explain this to me?
Comment: Yes, if you're staying with them, that's your address (at least while you're staying with them.)
Comment: Do you know yet what your US address will be? You might be overthinking this. As you're a citizen, I wouldn't expect most employers to care about whether or not you're in the US during the rest of the year. They just want you present when you're working, right?
Comment: @DanGetz I will be staying with family. Should I put their address as my own?
Comment: You will have to present your passport and Social Security card to your employer when you start work, so make sure you have both of these available.
Answer: Some things you can do:

Clearly indicate that you are a US citizen and are authorized to work in the US
Clearly indicate that you are currently living abroad, however you will be returning to the US on / before summer
Clearly indicate that you will need to interview via Skype / Google / whatever else, since you currently reside outside of the US. Indicate your time zone if you don't plan on just staying up for the interviews

The chief point is clearly indicating that you are a US citizen and can work legally in the US. But don't stop there, put some stuff in your cover letter about your adventures abroad, how they changed you, what you learned. Present yourself as a citizen of the world, it's an advantage :)
Answer: Applications are for people living in the US for reasons that is hard to get a visa for people that don't. But you don't need a visa, so this limitation doesn't apply to you.
Just write down a US contact address (I'm sure you have some friends or relatives in the US whose address you can give), and get a US phone number (Skype or Google Voice, or similar) and you're golden.


Does anyone have a .sh script to scan recursively the current folder for 0 byte files and place them into text file?

Question: I am looking for a simple .sh script which can scan the current folder and sub folders recursively for 0 byte files. I know this can be done in only a few lines, but I'm quite noobian on the command line of Linux.
It would be great if the output could be listed to a text file, like > 0byte.txt.
Answer: Use find command:
find /path/to/directory -type f -empty > zerobyte.txt

-type f look only for files
-empty finds empty files
Comment: thanks ! it works ! i changed the path so that i could scan the current folder and all of its subfolders  - find ./ -type f -empty > 0byte.txt


Pendulum clock, escapement pallet mounting position

Question: Im interested in creating a 3d printed pendulum clock,
all the diagrams and files I can find are mounting the pallet at the top of the escapement wheel which causes more complex design to avoid pendulum rod with the rest of the clock,
why cant the pallet be mounted downwards from the escapement wheel? is there any particular reason?
Comment: "Avoiding the rest of the clock" isn't really an issue, The traditional layout has the clock gears mounted in a frame, the face outside the front of the frame, the driving weights hanging below the frame, and the escapement and pendulum outside the back. That's a simple and logical layout.
Answer: If pallet was to be on the bottom it would tend to fall into the escape gear at the left and right of each tick tack, so it needed to have ballasts balancing it, which adds more inertia than the escape gear can handle.
While when it is positioned on top the connection to pendulum is naturally balanced with lighter assembly.


What does Menzoberranzan look like?

Question: Running a 5e campaign, I know a lot has changed about Menzo.  For instance Lolth is no longer the sole power with her children coming back.  My campaign is taking us to Menzoberranzan, but I don't really know how to describe it, or shops, or houses there.  I've been googling and searching all morning but I can't find more than the wikis.  The wikis are great but they describe history and events, not physical descriptions of architecture or the common goings on.
Comment: According to the color palette of the graphic novel versions of the R.A. Salvator stories, it's *very purple*.
Comment: In addition to the information in the answers given, you can probably get some good descriptive text and ideas from module D3, Vault of the Drow.  It's not Menzoberranzan, but Erelhei-Cinlu is the original Drow city.
Answer: I'd highly recommend that you purchase or borrow Out of the Abyss, since it is the only source of information about Menzoberranzan in 5th Edition of Dungeons & Dragons. The information is pretty huge and is about 20 pages long. There are lots of physical descriptions. Furthermore there is tons of material about the Underdark. If your adventure is taking place there, it would help you a lot.
Not to make you aggrieved, here is some crucial info:

Population: 20 000 drow plus thousands of slaves (of various races).
The government is a Matriarchal theocracy worshiping Lolth, the Demon Queen of Spiders.
The city has a large standing army of trained drow warriors and mages, bolstered by armed slaves and magical wards. The citizens themselves form a formidable militia.
You can easily purchase well-trained slaves, fungi, molds and exotic creatures for food (even ones imported from the surface), poisons, potions, oils and elixirs, jewelry, perfumes and silk.
The most important organizations are:

The ruling Council (comprised of the matron mothers of the eight most powerful drow noble houses in the city)
the Church of Lolth (based in Arach-Tinilith)
Breagan D'aerthe (company of drow spies, mercenaries and assassins)
Comment: Ah beat me to it! I'd add there is some physical descriptions for the city (and some other Underdark locations) in the Sword Coast Adventurer's Guide.
Comment: Thanks @Momonga-sama I actually own Out of the Abyss I just hadn't opened it yet!  That's exactly what I needed.
Answer: There is an early R. A. Salvatore Drizzt book set in Menzoberranzan: Homeland, the first book in the Dark Elf Trilogy. I seem to remember Drow using levitate abilities to gain access to buildings, but that was a long time ago, so I could be way off.
As I recall, the city is dominated by powerful houses which war with each other. I imagine the holds of the houses being build up in and upon massive stalagmites which support the cavern which houses the city, with hubs of housing and structures surrounding the base. The slums would be the areas furthest away from these seats of power.
Comment: Lore doesn't expire from one edition to another. Unless you have reason to believe something has fundamentally changed that would be reflected at the general architectural and everyday life level of Menzoberranzan, more detailed sources from previous editions are super helpful to people trying to flesh out the world.
Comment: Welcome to RPG.SE.   Please take the [tour] and visit the [help] to get a feel for how this Q&A site works.  The question is asking about Menzoberranzan in 5th edition, as opposed to previous lore.  Your answer would be improved by providing supportable information from the current edition/lore if you have access to any.  Citations and sources are encouraged in answers.
Comment: *Starless Night* would be another particularly good book to reference, as it's specifically got surface dwellers making their way into, interacting within, and getting out of Menzoberranzan.
Comment: Noble drow were able to use levitation (and had items to add additional uses of this daily power).  The nobles separated themselves from the commoners (most of whom did not have this power) by making the only way into the upper floors was to levitate to an upper balcony.
Answer: In May 2021, Wizards of the Coast (WoTC) published an animated short on YouTube, narrated by Benedict Cumberbatch, on their Dungeons & Dragons channel. The video is titled "Sleep Sound" and includes visual and audio references to Drizzt, Menzoberranzan, and the Drow. This short was done to drum up excitement for the WoTC-sanctioned video game, Dungeons & Dragons: Dark Alliance.
Some of the stills from that video include artistic depictions of Menzoberranzan. As this is an official video created and published by Dungeons & Dragons with input from R.A. Salvatore, I reckon it is safe to consider it a canon depiction of what Menzoberranzan looks like.

There's also a follow-up video by the D&D team where the interview R.A. Salvatore himself about the making of this animated short at https://www.youtube.com/watch?v=MNMRbRedKic
Comment: @nick012000 for what it's worth, the 8-pointed star depicting chaos goes back much further than the creation of Warhammer (and thousands of years further for depicting other things). Warhammer itself probably ripped it straight from works by Michael Moorcock. In fact, the symbol depicting chaos specifically was published in TSR's *Deities & Demigods* in 1980 for one of Moorcock's literary creations. I'm not super familiar with W40K but I think it came into existence as a spinoff of D&D, at least in terms of the minis.
Comment: The symbol on that banner looks an awful lot like the Star of Chaos from Warhammer...
Answer: For strict 5E material, you should stick to Momonga-sama's answer
.
But if you're still in need of ideas and inspiration, you could consider acquiring the Menzoberranzan: City of Intrigue supplement (may be hard to get a physical copy, but PDF is also available).
Chapter 4 in this supplement is devoted to the City of Spiders, spanning around 20 pages. This chapter includes tons of descriptions and a handful of illustrations (other than the ones in Lino Frank Ciaralli's answer).
Now, I mentioned this isn't quite 5E because it was published while 4E was the norm. And while this supplement is intended to be edition-neutral, it covers the period from -3917 DR to 1480 DR. Which means all of this happens before The Sundering.
On a final note, I've also found people recommending the 4E Underdark supplement (PDF). I don't own this one and I haven't read it, but it could be useful. (Thanks to @keithcurtis for pointing out that this supplement does not take place in the Forgotten Realms, nor is there any mention of Menzoberranzan)
Comment: I have the Underdark supplement. Although it is a wealth of information and adventure seeds, it does not take place in the Forgotten Realms, nor is there any mention of Menzobaranzan. There is a 4th edition book on the city specifically, though, with a poster map.
Answer: Great detail so far.  If I might add to it from even earlier sources:
In 2nd Ed there was a whole boxed set: Menzoberranzan - the Famed City of the Drow that is chocker block full of pictures and descriptions of the city.
For some visuals there was a video game that had some nice (for the time) graphics of both interior and exterior scenes in the city.
Answer: I would recommend the book series War of the Spider Queen. It contains much information about the different parts of the city, and special attributes about different areas within the city (like how the market area has spells of silence around it to prevent the noise from bothering the other parts of the city. That series also gives a detailed understanding of the non-drow races living there.  It was the book series that got me into DnD in fact.
Answer: Sword Coast Adventurer's Guide (p. 101) has a little blurb about the City of Spiders.
It is described as a vast cavern, about two miles long. One wall plateau is consumed by the Academy, Tier Breche, where young priestesses, soldiers, and wizards of the noble houses go to be educated. Many huge stalagmites climb toward the ceiling, and these are turned into dwellings, in much the same way surface elves coax trees into a desired shape rather than simply clearing them and building something from scratch.
Walled off in the center is the marketplace, where the Drow and others can conduct a brisk business, but the higher-up Drow don't need to deal with it if they don't wish to.
Rothe herds are raised a little ways off, and I'm sure some river flows nearby, to supply water. Though the Drow can see somewhat in darkness, the region is dimly illuminated by glowing fungus, so others can function as well.

What does Menzoberranzan look like?


Fork bend issue!

Question: I have a Pulsar 180 2016 model. I recently met with an accident and I replaced the doom and light set everything. Now when I leave hands from handlebar and drive, my ride control is missing and is slightly moving towards the left side. How do I figure out Whether my fork is bent or what else might be wrong? How would I fix it?
Comment: Does your handle shakes back and forth under braking? Please, don't leave hands and drive again.
Answer: I would go to a specialist to get the alignment checked, there could be damage that you cannot see with the naked eye. If the bike drifts to the lhs then something is not correct.
Answer: Something is out of line.. Depending on the accident and impact points,  perhaps first check just to make sure that the wheels & axles haven't been knocked out of alignment. Sometimes after a low speed crash or drop you can realign the forks if they're perhaps slightly twisted but its best to get someone who's got experience with this to do it.
If its more serious impact than a slight knock, you'd be best to have the bike checked for alignment properly. Forks and headstock take quite an impact in accidents and should be tested for damage & alignment with the proper equipment.
Answer: If the forks are really bad, you can sometimes see creases where the metal has folded. Bent forks can also be extremely subtle. To check them you need to take them apart and roll them on a flat, clean surface. Any bend will be apparent by a change in the profile between the fork stanchion and surface. This is really the DIY at home method of checking them. Professionals have very delicate and precise instruments for measuring forks.
It's possible to have forks straightened, although it can only be done with very subtle bends, and the cost for doing so is usually about the same as buying a good used set. There is also a risk that the strength of the forks have been compromised while being bent back and forth.
As mentioned in some other answers, I would start with trying to loosen the bolts around the triple tree and wheel and let everything realign. https://www.youtube.com/watch?v=IFV7ZJrORWw
It's also possible this is a problem with the headstock, or some other part of the frame.

Fork bend issue!


How does one check huge files identity if hashing is CPU bound?

Question: For small files hashing is just ok, but with huge ones you can easily find md5sum is CPU bound. Is there any hashing algorithm able to scale out on multiple cores? Any workarounds? Ideas? Anything? :)
Comment: _Huges ones_ is plural and can be scaled out to multiple cores by hashing more than one file at a time. One way to do that in the shell is using [GNU Parallel](http://www.gnu.org/software/parallel/)
Comment: did you tried fciv.exe in windows to compare if better suited to fit on multicore cpu ? (https://support.microsoft.com/en-ca/kb/841290)
Comment: @yagmoth555, nope. I rarely use Windows, mostly I don't use it, I'd say. From the description it looks unlikely it scales on SMP.
Comment: In my experience on hashing, bound is disk IO. At least for desktop. Besides of it, in big task usually many files can be hashed. So some files can be hashed in parallel.
Answer: Mine own best at the moment solution is:
parallel --block=512M --pipepart -a …HUGEFILE… --progress --recend '' \
  -k -j …NUMofProcessesSay4… md5sum | md5sum
— It should be noted that:

Resulting md5 hash isn't of the file, but rather of md5s of its parts but still it allows you to compare if replica is identical to origin
It also doesn't perform very good, specially when you use pipe and not file as input
parallel's --pipepart as I found out doesn't support disk partitions

So I'd love to hear other ways around as well.
Comment: Git version of GNU Parallel now supports block devices (on GNU/Linux at least). Thanks for the idea.
Comment: This should have been put as part of the question rather than as an answer.
Answer: Unfortunately, MD5 is a linear process where its state depend on all the previous input. In other words, you can't truly parallelize it. Moreover, I'm not aware of any real hash alg that does not operate in this manner.
What you can do (and, based on your answer, you are doing) is to split the source files and concurrently calculate each chunk's md5sum.
If you can't/wan't do that, you had to use a faster hash function as xxHash, CityHash or SpookyHash
Other idea (maybe it is applicable to your intented usage): if you need something faster than MD5 (albeit single-threaded), you can use CRC32 (which is hardware-accelerated by recent CPUs) for a first fast pass, resorting to MD5/SHA1 for a second pass on seemly identical files.
Comment: The most valuable part of your answer (others is just boring repeating) is the list of possibly faster hashes. Thanks anyways.
Comment: BTW: http://stackoverflow.com/questions/10726325/can-md5-be-broken-up-to-run-across-multiple-cores-threads#comment13932768_10726325
Comment: @poige Did you read the other comments in the thread you linked? In the context of a single-input hashing, MD5 can not be parallelized, simply because it is a linear process (ie: current state depends on previous inputs).
Comment: I won't consider this as correct answer. ;-P
Comment: @shodanshok the issue with the second approach is that for a valid matching of a large directory with many large files, is that if all files are identical, you are adding a lot of overhead and still running md5sum on every file.
Comment: @Jedi sure, it is only a quick workaround for the non parallelizable nature of MD5. It many files are identical, you may end up with slowdown.
Answer: There's pretty much no getting around processing the entire file. MD4 or CRC32 are probably your best bets for a widely deployed and fast algorithm (though CRC32 is going to be far less effective than MD4).
Testing various implementation of your algorithm of choice will help. If you can find a well-tested asm implementation, it will likely improve upon the performance of its C/C++ cousins.
If you don't really care about interoperability, hashing across multiple cores is easily doable by splitting the file into chunks (doesn't need to be done on-disk, you'd just start reading from specific offsets) and processing each chunk separately (this will result in serious disk thrashing though, degrading the performance, especially for mechanical disks). You'll end up with separate hashes for each chunk (though this has other advantages, like pointing you toward the broken chunk) but you could always hash them together for one final value.
This Gist could be a good start for something in Python.
Comment: I didn't say it's impractical; but it's not practical cause you don't have anything in your answer that can be used right away. For e. g.: this is practical answer: http://serverfault.com/questions/488486/debian-port-80-is-blocked-but-i-dont-know-by-what/488491#488491
Comment: `split` does indeed comes to one's mind, but, alas when we talk about huge files (as we do) it's not an option.
Comment: @poige As I said, you wouldn't do it on disk, just start hashing the file from specific offsets and stopping at the start of the next chunk.
Comment: Yeah, but that's the theory which is quite obvious; anything practical?
Comment: @poige From your question I can't guess at why that approach would be impractical. Perhaps there's a constraint you forgot to include?
Comment: I won't consider this as correct answer. ;-P
Answer: Most of the answers here have addressed the linear nature of most hashing algorithms. Although I'm sure there exists some true scalable hashing algorithms, an easier solution is to simply split the data up into smaller pieces, and hash each individually.
Consider the BitTorrent approach: When a Torrent is created, all of the files are split into 'blocks', each block individually hashed, and each of those hashes recorded in the .torrent file. This is what allows a peer to incrementally verify incoming data, without having to wait for the entire file to finish downloading first. Errors can also be corrected on a per-block basis, instead of requiring re-transmission of the entire file. Aside from the logistical benefits, this approach also allows hashing to scale across multiple cores - if 8 cores are available, 8 blocks can be simultaneously hashed.
If you engineer your verification process to work on some subset of the data, e.g. blocks of some fixed size, you can hash each block on a separate core, thus eliminating a large amount of delay in the pipeline. Obviously, this approach has a small time/memory trade-off: each additional instance of hashing has some overhead associated with it, mostly in the form of memory, although this is minimal unless you're running hundreds of instances.
Answer: I'm working on a tree hashing project, which is designed for exactly this problem: off-the-shelf parallel hashing of large files. It works now, though it hasn't been reviewed, and there's a good chance that changes from review will result in changes to the final digest. That said, it's very fast: https://github.com/oconnor663/bao
Answer: You can use md5deep for this and hashdeep for other hashes. It supports multi threading with the -j flag. By default it will create a hashing thread for each core. It also has a flag to break files into pieces before hashing but will not use multiple threads on a singe file. I've used this for getting sha256 of half a million files and it worked great. It also has a recursive flash which makes handling large directory trees easier.
Here is the manpage for it http://md5deep.sourceforge.net/md5deep.html and git repo https://github.com/jessek/hashdeep
The package name in ubuntu and debian is md5deep and includes hashdeep.
Comment: From the man page I'd expect `-j` to support thread per each file given, not its parts.
Answer: It's easy to design a hashing algorithm that is scalable over multiple cores, it's just that the best known hashing algorithms tend to be designed specifically to prevent that, in order that tasks like finding hash collisions are made as slow as possible.
Hashing functions that don't force serial processing may suit you, but that depends what properties you expect of your hashing function.  As such, I don't think that you've given enough information for a good recommendation to be made.
As others have suggested, you can construct a hashing function as the hash of the concatenated hashes of each of the blocks of some given size in the original.  So long as the block size is large enough to make it difficult to reverse the hashes of individual blocks, this is likely to work well enough for most purposes.  How big that should be depends on how predictable the content of those blocks is.  If you are able to estimate the entropy, and choose a block size such that you get 128+ bits of entropy per block, that should be sufficient for most purposes (and overkill for many where security is not the primary concern).
From a security point of view, you are concerned about the degree of entropy at the block level, because otherwise finding a collision for a single block is enough to enable a malicious actor to substitute part of the content and get the same final hash.
It's perhaps worth noting that having a fixed block size means that the main weakness of MD5s is irrelevant - the hacker cannot append extra data to the block.
If your needs are about preventing naturally occurring hash collisions as opposed to malicious ones, then you can no doubt afford to use a much faster checksum function.  Cryptographically secure hashes are typically designed to be slow to calculate.
A function from the skein function group using the optional hash tree mode might suit you.  Then again, CRC32 might be all you need.
Comment: I could throw in some stuff about the controversy around SHA-3 (i.e.Keccak) if you like, but perhaps you should just read it on wikipedia.


Above Minus value vacuum

Question: If we speak about vacuum above -25mbar, does it mean that it shall be deeper than -25mbar, i.e., for example, -40mbar?
Answer: My gut feeling for this question as it is worded is that yes, a vacuum above -25 mbar means that it shall be deeper than -25 mbar, e.g. -40 mbar.
When measuring a vacuum the scientific community (to the limit of my experience) would normally use absolute values, so between 0 bar and 1 bar. A total vacuum is considered to be 0 bar. By comparison, atmospheric pressure at STP (standard temperature and pressure) is 1 bar. The vacuum of space is just slightly above 0 bar. (Also in my experience it would be measured in Pa, but that's not in scope here.)
When vacuums are referenced as negative values this often refers to a suction pressure value as it is referenced to atmospheric pressure. This can also be slightly variable since local atmospheric pressure is variable, unless it is a controlled environment.
This also leads to the uncertainty of the meaning as you have asked due to the ambiguity in definition.
Consider this:
A suction pressure of 25 mbar gives a vacuum of -25 mbar when referenced to atmospheric pressure.
But... a suction pressure greater than 25 mbar gives a vacuum below -25 mbar.
A suction pressure of 30 mbar gives a vacuum pressure of -30 mbar, which is lower than -25 mbar, but which might also be considered to be above -25 mbar, and could also be spoken of as being greater than -25 mbar. Which all just leads to confusion, which leads scientists to sometimes go to great pains to be precise in their meaning, but that meaning can be sometimes quite different to the everyday meaning, which brings us back to square one (if we are not aware of this).

Above Minus value vacuum


How can I connect my Nokia Lumia 520 with Ubuntu 14.04?

Question: I cannot seem find a way to connect a Nokia Lumia 520 to Ubuntu 14.04. I tried several solutions posted on the Internet, but I could not find the right one. Has someone achieved this?
Comment: have you used bluetooth connections too???
Comment: It would be really helpful if you could edit your question to include exactly what you have tried and how it failed (including any relevant messages like errors, warnings, etc).
Answer: The author of this project: Android File Transfer For Linux luckily for me agreed to add WP8 support and now this is the only solution that reliable works, afaik.
Now it's able to connect my Lumia 1020 WP8.1 Denim and Kubuntu 15.04 via
usb.
Of course, device shall be unlocked with correct PIN beforehand.
The project is a library and has simple GUI which is mostly for library demonstration and testing purposes, so don't blame it for UX.
Comment: I confirm this works even for my Lumia 730, which is only detected as PTP in 14.04 and later releases with the same libmtp version (I assume our devices will have been replaced when fixes for such devices make it out of the development tree into an OS release ヽ(◕﹏◕)ノ ). Good find and good job you did there.
Answer: How to connect Lumia 520 Windows Phone (WP) (Windows 8.0 - Amber) to computer (Ubuntu 14.04):

Download Pocket File Manager (PFM) to WP from Store. PFM has a free version so no need to buy the full version within the app.
Turn on computer - do not enter password yet
Turn on phone - turn on pocket file manager
Connect phone to computer via USB
Enter computer password - computer is now fully on
Click phone icon launcher on computer
The phone and SD card will be displayed and file operations can be used in the normal way
Once tasks completed, keep the phone attached via USB and shut down the computer - Do NOT turn off computer file manager
Once the computer has shut down, remove phone USB

Notes:

If you do not use a password to open Ubuntu because you automatically  start the computer then turn on the phone, open PFM and connect the phone via USB before switching on the computer
Please note that the Cyan update (Windows 8.1) is imminent apparently. Cyan will have it's own file manager so PFM may not be necessary. Possibly the new file manager will mean that the current work around is superfluous too.

Bluetooth works too as already mentioned.
Answer: To transfer files between your computer and phone you can run a server and access it via the phone browser. I have started a project on github- clouder-lite, give it a try!
PS: Python3 is available on Ubuntu14+ by default.
Answer: Alternatively to what nigel said, you may want virtualize windows in virtual machine if you have no access to the OS.
In fact this is quite a useful option to run programs like microsoft office, autocad and itunes; microsoft even made windows freely downloadable.
To do this you have to download virtualbox from the software center and then follow this tutorial: http://pclosmag.com/html/issues/201309/page15.html
Pay attention however to the fact that the license lasts only 90 days and then you have to restore the virtual machine from a snapshot or a backup.


Can my Mobile wallet company steal my coins?

Question: My mist-wallet is used for purely for dapp development. To fuel my future ambitions, I went to an online exchange and bought some ether coins and used a mobile-only wallet for these real ether. When trying to research how a mobile wallet differs from Mist-wallet, it seems mobile wallet is a contract and my mobile wallet company participates on my behalf in EVM. If this is the case, how can I trust my mobile wallet company? Can my mobile wallet company transfer all the currency I got into their own and blame it on hackers? TIA
Comment: You can choose a mobile wallet company with 2-of-2 signature. This means that a transaction needs to be signed by 2 private keys - yours and the company's. This way, the company alone cannot send transactions/transfer ether without your consent. Check [Multisignature](https://en.bitcoin.it/wiki/Multisignature).
Answer:
If this is the case, how can I trust my mobile wallet company?

Unless you know specifically the details of the contract's code you can't (you can get the EVM byte code from the block chain by knowing the address at which it has been deployed to).

Can my mobile wallet company transfer all the currency I got into their own and blame it on hackers? TIA

It depends on how the contract was written as contracts can send balances to other contracts.
Comment: I can understand for Ethereum, there may be soft contracts. How are wallets like JAXX manage bitcoin wallets? There were no contracts on bitcoin blockchain. Isn't it?
Comment: I haven't used JAXX. No, bitcoin does not have Turing complete scripting language like Ethereum.
Answer: Just did a bit more research and came to know that MIST is both a node and a wallet whereas JAXX is just a wallet and not a node. Basically, JAXX server is a node and creates accounts for each of the wallet customers. So, it's better to use only reputed wallets. As any wallets server node implementation isn't open source, there may be a chance that server source can look deep into your keys when you do transactions at a node related to your wallet. My 2 cents.


Is it possible to get the raw IR image data from the Superframe?

Question: I am using the java API with the Tango Peanut phone, and I wanted to know if there is a way to get the raw IR image from the RGB-IR camera that the depth sensor uses.  I know that a quarter of the pixels from the RGB-IR camera is IR data.  I also know that all of the 4MP RGB-IR image gets put into the superframe and then converted to YUV. However it was unclear on how to decode the IR channel, or if it is even possible at this point.  If its lost inside the YUV superframe, is there any other way I can retrieve the raw IR image?
Comment: How do you know that IR sensitive data can be extracted from YUV raw frame? By IR sensitive channel, I mean a one channel image that can see emitted IR pattern (not the Depth channel).
Answer: In order to get the depth data:

http://www.pocketmagic.net/wp-content/uploads/2014/05/sbrl.zip
taken from http://palcu.blogspot.ro/2014/04/google-project-tango-hackathon-in.html

You might also wanna try

https://github.com/googlesamples/tango-examples-c/wiki/Depth:-Point-Cloud-Viewer
http://www.pocketmagic.net/2014/05/google-tango-hackathon-in-timisoara/#.VCQ6H1eHuiN

Please keep me posted on success/failure. Are you on a tablet or phone?
Comment: according to a someone at google tango, their API doesn't support a way of getting RAW IR image


How to use Node.js to build pages that are a mix between static and dynamic content?

Question: All pages on my 5 page site should be output using a Node.js server.
Most of the page content is static. At the bottom of each page, there is a bit of dynamic content.
My node.js code currently looks like:
var http = require('http');

http.createServer(function (request, response) {

    console.log('request starting...');

    response.writeHead(200, { 'Content-Type': 'text/html' });

    var html = '<!DOCTYPE html><title>My Title</title>';
    html += 'Some more static content';
    html += 'Some more static content';
    html += 'Some more static content';
    html += 'Some dynamic content';
    html += '';

    response.end(html, 'utf-8');

}).listen(38316);

I'm sure there are numerous things wrong about this example. Please enlighten me!
For example:

How can I add static content to the
page without storing it in a string as a variable value with += numerous times?
What is the best practices way to build a small site in Node.js where all pages are a mix between static and dynamic content?
Answer: Personally, I'd use a server that has higher level constructs. For instance, take a look at the expressjs framework - http://expressjs.com/
The constructs you'll be interested in from this package are:

Truly static files (assets etc): app.use(express.static(__dirname + '/public'));
A templating language such as jade, mustache, etc:

http://expressjs.com/en/guide/using-template-engines.html
https://github.com/visionmedia/jade/
You'll want to look up 'locals' and 'partials' for embedding small bits of dynamic content in mostly static content

For example in jade:
!!! 5
html(lang="en")
  head
    title= pageTitle
    script(type='text/javascript')
      if (foo) {
         bar()
      }
  body
    h1 Jade - node template engine
    #container
      - if (youAreUsingJade)
        p You are amazing
      - else
        p Get on it!

Becomes:
<!DOCTYPE html>

    <title>Jade</title>

Jade - node template engine

You are amazing

If you prefer something a little less drastic I would say look at mustache or one of the other engines that looks a bit more like regular-sauce html.
Comment: I ended up using express with ejs. I created the dynamic content on app.js (file created by express express) var foo = "bar".... Then I added the  dynamic content in the app.js file in the statement: res.render('index', { my_dynamic_content: foo }); ... Then I added the content to my html page (index.ejs) with <%= my_dynamic_content %>
Comment: Second link is broken.
Answer: Alternative you can just use jsDOM. This means you have a DOM object you can manipulate on the server to add your dynamic content, then you can just flush the DOM as a HTML file / string
Answer: These days the answer is not so straightforward.
If you don't need to be indexed by Google, consider making a single-page application using socket.io and client-side templates such as jQuery Templates. There are even emerging node.js frameworks for this type of architecture, e.g. socketstream.
If you need to be indexed by Google, do you need your dynamic content to be indexed? If yes,
consider using express and server-side templates such as ejs, jade or mustache. Another (discouraged) approach might be to generate XML from JSON on server and use an XSLT front-end.
If you need only static content to be indexed, consider using express on server, but don't generate any dynamic HTML on server. Instead, send your dynamic content in JSON format to client using AJAX or socket.io, and render it using client-side templates such as jQuery Templates.
Don't consider server-side DOM: DOM doesn't scale for complex layouts, you will sink in a sea of selectors and DOM calls. Even client-side developers understood that and implemented client-side templates. A new promising approach is weld library. It offers best of both worlds, but it is not mature yet to be used in production (e.g. simple things like conditional rendering are not supported yet).
Answer: One good way is to use a templating engine.  You can store the templates as separate files, and the templating engine has the ability to make the content dynamic.  Personally I use yajet (http://www.yajet.net/) which is written for the web but works fine with node, and there are numerous template engines for node on npm.
Answer: One of the best things I found is to use NodeJS, Express and Mustache...
You can create your HTML pages as you normally would using Mustache syntax for placeholders for your variables {{name}}...
When a user hits your site, express routs the slug to the correct template...
NodeJS get's the file...
NodeJS get's the dataset from a DB...
Run it through Mustache on the server...
Send the completed page to the client...
Here is a scaled back version I wrote on my blog.  It's simple but the idea is pretty sound.  I use it to quickly deploy pages on my site.
http://devcrapshoot.com/javascript/nodejs-expressjs-and-mustachejs-template-engine
I went this route because I didn't want to learn all of the extra syntax to write a language I already knew (html).  It makes more sense and follows more of a true MVC pattern.
Answer: First deliver only static HTML files from server to the client. Then use something like AJAX / server.io to serve the dynamic content. IMO Jade is really ugly for writing HTML code and its better to use a template engine.
I did some Google and found some code by this fellow, its good if you are doing it for PoC / learning.
var server = require('./server');
var controller = require("./controller");
var urlResponseHandlers = require("./urlResponseHandlers");

var handle = {};
handle["/"] = urlResponseHandlers.fetch;
handle["/fetch"] = urlResponseHandlers.fetch;
handle["/save"] = urlResponseHandlers.save;
server.start(controller.dispatch, handle);

Here is how the logic for handling URLs is displayed -
var staticHandler = require('./staticHandler');

function dispatch(handler, pathname, req, res) {
  console.log("About to dispatch a request for " + pathname);
  var content = "Hey " + pathname;
  if (typeof handler[pathname] === 'function') {
      content += handler[pathname](req);
      res.writeHead(200, {
          'Content-Type': 'text/html'
      });
      res.write(content);
      res.end();
  } else {
      console.log("No request handler found for " + pathname);
      staticHandler.handleStatic(pathname, res);
  }

}
Here is how static files can be handled -
function handleStatic(pageUrl, response) {
    var filename = path.join(process.cwd(), pageUrl);
    path.exists(filename, function (exists) {
        if (!exists) {
            console.log("not exists: " + filename);
            response.writeHead(404, {
                'Content-Type': 'text/html'
            });
            response.write('404 Not Found\n');
            response.end();
            return;
        }
        //Do not send Content type, browser will pick it up.
        response.writeHead(200);
        var fileStream = fs.createReadStream(filename);
        fileStream.on('end', function () {
            response.end();
        });
        fileStream.pipe(response);
        return;
    });
}
exports.handleStatic = handleStatic;

I liked the idea. All code copied from this link!
.
Answer: A solution have found to this, without using any other modules and or other script is to make the calling script into a module and include it with the function require().
With this solution I can use javascript which ever way I want
What I would do is make an ajax call to a nodejs script (www.example.com/path/script.js)
script.js would need to be built like a module with the exports.functionName=function(){...}
After that include it in your webserver function require(pathToTheScript).functionName(res,req)
You will also need to end the response in the functionName(res,req) by doing res.end();


What is the formula for variance in estimating exchange rate?

Question: I was watching this Youtube Video. He used a exchange rates of Euro to Dollar for a few days and apply GARCH(1,1) to get the predicted price. However, I didnt understand variance that he calculates from the table. WHat is the formula?
Answer: GARCH model is used to model persistence in volatility. If you square demean exchange rate and calculate autocorrelation you will find significant autocorrelation  upto many lags that indicates the clustering of volatility in data.
A simple ARMA(1,0)-GARCH(1,1) model can be written as :
$$y_t=\mu + \phi y_{t-1}+e_t $$
$$e_t \sim N(0, \sigma^2_t)$$
$$\sigma_t^2=\gamma + \beta e_{t-1}^2+ \eta\sigma_{t-1}^2$$
After calibrating the above model, you can use the first equation to forecast one day ahead exchange rate(expected exchange rate). For example:
$$\mathbb{E}(y_t|\mathscr{F_{t-1}})=\mu_t+\phi y_{t-1}$$
Similarly, using last equation you can get conditional standard deviation. To get unconditional variance take expectation one more time:$$\mathbb{E[\sigma_t^2|\mathscr{F}_{t-1}}]=\gamma + \beta \, \mathbb{E}[e^2_{t-1}]+\eta \,\mathbb{E}[\sigma^2_{t-1}]$$
solving above equation, you will get
$$\sigma_t^2=\frac{\gamma}{1-\beta -\eta}$$


How do we know the Temple Mount is the location of Solomen's Temple

Question: There is some archeologist that claim that the western wall is not part of The Holy Temple and that its actually a fortress wall of the romans,instead they claim the location
of Beit HaMikdash is in the old city of David.
Comment: Can you link to any information about these alleged archeologists? I don't think they exist
Comment: Noone claims that the *Western Wall is anything other than part of the retaining wall built by Herod as part of his rebuilding effort.
Comment: There is a guy named Robert Cornuke who wrote a book about his theory of the Temple being south of the Mount. He describes himself as a Biblical archaeologist, but has no formal training(surprise!)
 and is the President of the "Bible Archaeology Search and Exploration Institute". Some of his points are listed on a Xtian site page: http://waytojesus.org/site-solomons-temple-south-temple-mount/   . There may be a renegade archaeologist or two with the same theory, but it's pretty much impossible, since real archaeologists have uncovered the wide staircases of ascent going UP to the Mount.
Comment: As far as what IS there, Dr Mazar's current excavations south of the Mount have uncovered a large royal/administrative complex, parts of it dating back to the United Monarchy.  She;s been working there for years, and thanks to pottery and other clues, is able to pinpoint the dating of stuff there to within 50 years or so.
Answer: The Western Wall was constructed by Herod in order to serve as a retaining wall for the actual Temple Mount. It was not part of the Temple or temple mount, but was the closest Jews were allowed to approach by the gentile rulers.
Western Wall

The Western Wall in the midst of the Old City in Jerusalem is the
  section of the Western supporting wall of the Temple Mount which has
  remained intact since the destruction of the Second Jerusalem Temple
  (70 C.E.). It became the most sacred spot in Jewish religious and
  national consciousness and tradition by virtue of its proximity to the
  Western Wall of the Holy of Holies in the Temple, from which,
  according to numerous sources, the Divine Presence never departed. It
  became a center of mourning over the destruction of the Temple and
  Israel's exile, on the one hand, and of religious - in 20th century
  also national - communion with the memory of Israel's former glory and
  the hope for its restoration, on the other. Because of the former
  association, it became known in European languages as the "Wailing
  Wall".

The claim that you refer to was not made by archeologists, but by Arab fanatics attempting to deny any connection of the Jews to the land of Israel (even when ithat claim contradicts their own books).
'Western Wall was never part of temple'  By MIKE SEID October 25, 2007

The former mufti of Jerusalem, Ikrema Sabri, has made the claim that
  there never was a Jewish temple on the Temple Mount, and the Western
  Wall was really part of a mosque.

Of course he lied

Archeologists overseeing Islamic infrastructure work on the Mount
  announced this week that they had unveiled a sealed archeological
  level dating back to the First Temple period. The First Temple was
  built by King Solomon in the 10th century BCE, and destroyed by the
  Babylonians in 586 BCE. The Second Temple was built 70 years later,
  enlarged during the first century BCE by Herod, and destroyed by the
  Romans in the year 70. The Dome of the Rock and Al-Aksa Mosque were
  constructed on the Temple Mount site in the late seventh century.

Archaeologists spotlight first Solomon's Temple-era artifacts ever found on Temple Mount.

Israeli archaeologists on Thursday presented new details of what they
  said were the first tiny artifacts, unearthed in situ on the Temple
  Mount, ever conclusively dated to the time of the First Temple over
  2,600 years ago. The discoveries were made during limited scientific
  excavations carried out atop the flashpoint Temple Mount in the past
  decade, the first of their kind since the British Mandate.

Many first and second temple era relics have been found in spill that the Arabs have attempted to throw away while carefully trying to destroy any evidence that might be found connecting the Temple Mount to the Jews.
Jerusalem's Temple Mount Flap

A group of archaeology students examined Temple Mount fill dumped by
  the Waqf in the nearby Kidron Valley and recovered ceramic material and
  architectural fragments dating to this period and later.
Comment: Thank you so much, may the Moshiach come quickly in our time.