Default country settings in OS X 10.9.1

Question: I have a very annoying problem with my Mac. My default country is somehow set to the Netherlands. Whenever I open Google with Safari or another Web browser, I get redirected to google.nl. I also cannot use my Spotify account anymore because it says that I need to be in my home country. How can I change that? I already tried using System Preferences -> Language & Region, but that does't work.
Answer: Google and Spotify are most likely showing you Netherlands information because they are associating your IP address to a location in the Netherlands.
This isn't a setting that is controlled from your browser, but is a component of your internet connection that services use for various reasons to personalize the experience to the user, without knowing much (yet) about the user themselves.
For example, if I VPN (tunnel my internet connection to make it look like I'm from a server physically located elsewhere) from the US to the UK, Google automatically directs me to the UK Google page, and I can watch Al Jazerra English and BBC. (both unavailable-ish in the US) Similarly, those services think you are physically in the Netherlands, and they behave accordingly; Google directs you to it's .nl service, and Spotify likely doesn't have streaming agreements in the country, so it cannot legally service those in the Netherlands.
Now, you don't mention where you are physically, so it is possible that you are not physically in the Netherlands, but whatever service Google and Spotify use to associate an IP with a general location says that you are, likely because (some time in the past) that IP address was associated with a location in the Netherlands. If that's the case ... you may need to contact your ISP to see if they have a remedy for this kind of problem.
Comment: I'm from Germany. Indeed I was in the Netherlands for a couple of weeks, but that was month ago. Ok, I will contact my ISP and see if they can help me.
Comment: How can I check on OS X If I'm using a proxy?
Comment: System Preferences > Network; choose the method you're connecting with on the left and go to "Advanced...". You'll see a proxy tab.

Default country settings in OS X 10.9.1


Ramsey Numbers and the Probabilistic Method

Question: I am trying to prove that if there exists a real number $0 < p <1$ such that
$$\binom{n}{k}p^k + \binom{n}{q}(1-p)^q < 1$$
for some $k, q \in [n],$ Then $R(k,q) > n.$ I see by the construction of
this problem that they are suggesting some form of probabilistic method, i.e.
on a random edge 2-coloring of the graph $K_n,$ where the probability of an
edge getting the color $1$ is $p$ (and thus the probability of an edge getting
the color $2$ is $1-p$),
$P(\text{Getting a monochromatic } K_k \vee
\text{Getting a monochromatic } K_q) < 1.$
The tough part is finding this particular probability. I can see by the
definition of a union of events that
$$P(\text{Getting a monochromatic } K_k \vee
\text{Getting a monochromatic } K_q)$$
$$\leq P(\text{Getting a monochromatic } K_k)
+ P(\text{Getting a monochromatic } K_q),$$
But I am having issues with both of the counting proofs for this particular
part of the problem. Any suggestions?
Answer: I think your statement is false, for example it would imply $R(k,2)>k$.
I could only show that $R(k,q)>n$ when given that for some $p\in(0,1)$ we have the weaker inequality
$${n\choose k}p^{k(k-1)/2}+{n\choose q}(1-p)^{q(q-1)/2}<1.$$
In $K_n$, colour every edge independently, with probability $p$ colour it blue and red otherwise. For every $K_k\subset K_n$, there is a probability of $p^{k(k-1)/2}$ that $K_k$ is completely blue. Hence the expected number of blue $K_k$'s is ${n\choose k}p^{k(k-1)/2}$. Similarly, the expected number of red $K_q$'s is ${n\choose q}(1-p)^{q(q-1)/2}$.
Because ${n\choose k}p^{k(k-1)/2}+{n\choose q}(1-p)^{q(q-1)/2}<1$, there is a particular colouring of $K_n$ with no blue $K_k$ or red $K_q$, thus $R(k,q)> n$.


RCA TABLET RESET

Question: I am trying to reset my rca tablet. I just want to clean everything off. I tried holding the volume and power button. I told until dogs come up, then screen goes black for a second then dogs just come up again then goes black again then dogs. Then the regular log in screen comes up.
Comment: You were told to hold volume up button them briefly press the power button. Keep pressing the volume button.
Answer: Follow the instructions below to reset your RCA Tablet (Should work for every RCA models)

With your tablet turned off, press and hold the volume up (+) button. While holding the volume up (+) button, press the tablet's power button until you see the RCA logo with Nipper and Chipper on the screen. After a few seconds, the screen will change and you will see the Android bot on his back with a caution symbol above it.
Now  press and hold the  power button, and without releasing the power button press down on the volume up (+) button.
Use the  volume up (+) and down (+) keys to navigate to and select the "wipe data/factory reset" option. To select this option, press the power button.
The device should ask you to confirm your selection. Use the  volume up (+) and down (-) keys to navigate to and select "Yes – delete all user data." Once again, use the power button to select this option.
 At the bottom of the next screen, you will see "Data wipe complete." Press the power button to restart the device.
The device should begin to reboot and once again display the RCA logo with Nipper and Chipper. The next "Welcome" screen will prompt you to select your language of choice. Scroll through the options using your finger and press start when finished..
Comment: Actually it says hold power button UNTIL the screen changes, it does NOT say briefly hold the power button while still holding volume up, HENCE the confusion, so you might want to edit those instructions.

RCA TABLET RESET


How to deal with an employee who craps on the toilet?

Question: We have an employee who doesn't wash his hands and now has been found to have left #2 on the bathroom toilet rim.  How do we address?
Comment: I hate to ask for details, but is this just a bit (evidence of carelessness) or a lot (evidence of a psychological problem)?
Comment: Final duplicate vote cast. Given the lack of detail here this reads like an exact duplicate of the linked question and that also got closed for not having a clear goal in mind. If there's some specific issue you're facing and there are elements that set this question apart from the linked one, please [edit] those in to nominate this for reopening.
Comment: Yuck. I will just plain speak to that person, in private, to be more serious with the hygiene of the workplace.
Comment: Tell him to cut it out and if he doesn't, fire him? Or if this was some sort of bizarre protest to being asked to wash his hand just fire him outright? This would seem to fall squarely within "Management 101". What kind of advice are you looking for here? Why aren't you already enforcing consequences on his behaviour?
Comment: The linked question is about #1 and this question is about #2, so they're not duplicates.
Answer: If you have some kind of public line of communication for your department or office (Slack, Gmail, Skype, etc.), I would send a gentle reminder to clean up after yourself in the bathroom. No names or specifics, just a blast message that could be about anyone. There's a good chance he might not even be aware that people are noticing and the fear that you may come for him directly may be enough for him to stop.
Comment: We sometimes have communications like this at our company (most often after people leave the communal coffee areas in a mess).  There's a reminder that cleaners only visit once a day (after working hours), so people cleaning up after themselves helps keep things looking nice for employees and visitors.  Perhaps a reminder about the cleaning schedule and the need for other people to use the bathroom might be useful here...
Comment: Please no, let's not encourage more of this non-management. Everyone will know who this is about *except* the person you're trying to reach. This should be managed directly.
Comment: This is a common courtesy issue. Things only get more complicated when involving management/HR. Now if this doesn't make him stop, by all means, bring it up with HR or to him face to face. But there's no need to make a federal case out of it.
Answer: This might warrant a write-up in the employee's HR file for creating or contributing to unhealthy or unsanitary conditions within the workplace.  It's no different than bringing one's personal issues to work, or committing a crime there because it affects the morale of everyone around.
So, get a paper trail started.
Comment: I don't know if it needs to go this far just yet. Looks like he/she has bad habits that needs to be brought up. I would agree to go this far if they tried all methods to ask him/her to be more clean and yet he/she refuses.
Answer: The most important question is: are you in a business (e.g. food industry) where an employee not washing his hands/keeping the hygiene actually is a big problem for the certification of you plant (although i am not sure bathrooms are inspected) or the safety of the customers/consumers?

If yes -> answer from Xavier J
if no -> answer from Brandon Wilcox


Dynamic input fields in WordPress Plugin

Question: I am trying to create dynamic input fields in a plugin I am working on. I want to add functionality to "Add/Remove and Save" options in my plugin. Something like the below attached.
Answer: For add and remove button functionality you have to use the jquery. Please see the code here => http://jsfiddle.net/lemonkazi/re8e2yov/
For save button you can use the form or ajax to save the data in option table.


MPMoviePlayerController Stack Overflow

Question: I'm trying to use MPMoviePlayerController in a fairly simple iPhone app.  The basic layout is an UIApplicationDelegate associated with a UIWindow xib file.  Within the applicationDidFinishLaunching method, I'm trying to play a movie with the following code:
// Path to the movie
NSString *path = [[NSBundle mainBundle] pathForResource:@"logoscreen" ofType:@"m4v"];
movieURL = [NSURL fileURLWithPath:path];

// Setup the player
moviePlayer = [[MPMoviePlayerController alloc] initWithContentURL:movieURL];

// Use the new 3.2 style API
moviePlayer.controlStyle = MPMovieControlStyleNone;
moviePlayer.shouldAutoplay = YES;
[window addSubview:moviePlayer.view];

[moviePlayer setFullscreen:YES animated:YES];

When this executes, I get an "EXC_BAD_ACCESS" error, and the GDB loads a huge stack (with the "_makeSubtreePerformSelector" method repeating several thousand times:
#6633   0x34b0cb0c in -[UIView(Hierarchy)         _makeSubtreePerformSelector:withObject:withObject:copySublayers:]
#6634   0x34b0cb0c in -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:]
#6635   0x34b0cb0c in -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:]
#6636   0x34b0cb0c in -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:]
#6637   0x34b0c9c4 in -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:]
#6638   0x34b0c790 in -[UIView(Internal) _addSubview:positioned:relativeTo:]
#6639   0x34b0c408 in -[UIView(Hierarchy) addSubview:]
#6640   0x33f81928 in -[MPInlineVideoViewController _transitionToFullscreenAnimated:]
#6641   0x33f7df5c in -[MPInlineVideoViewController setFullscreen:animated:]
#6642   0x33f05998 in -[MPMoviePlayerControllerNew setFullscreen:animated:]
#6643   0x33f059cc in -[MPMoviePlayerControllerNew setFullscreen:]
#6644   0x33f06b2c in -[MPMoviePlayerController setFullscreen:]
#6645   0x00002ab0 in -[GiyapLiteAppDelegate playMovie:] at GiyapLiteAppDelegate.m:67
#6646   0x000028a2 in -[GiyapLiteAppDelegate applicationDidFinishLaunching:] at GiyapLiteAppDelegate.m:38
#6647   0x34b16154 in -[UIApplication _callInitializationDelegatesForURL:payload:suspended:]
#6648   0x34cc46d4 in -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:]
#6649   0x34b7f7c0 in -[UIApplication handleEvent:withNewEvent:]
#6650   0x34b7eebc in -[UIApplication sendEvent:]
#6651   0x34b7e7f0 in _UIApplicationHandleEvent
#6652   0x33910ee4 in PurpleEventCallback
#6653   0x322352b2 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__
#6654   0x322371dc in __CFRunLoopDoSource1
#6655   0x32238194 in __CFRunLoopRun
#6656   0x321df0c2 in CFRunLoopRunSpecific
#6657   0x321defd0 in CFRunLoopRunInMode
#6658   0x34b0ab20 in -[UIApplication _run]
#6659   0x34b08fc0 in UIApplicationMain
#6660   0x000026f8 in main at main.m:14

It's worth noting that if I try the code that plays the movie based on a click event, it works just fine.  It's almost like the application hasn't finished "wiring" something up yet in regards to the window hierarchy?  Has anyone encountered anything like this before?
Answer: Maybe you should try setting animated to No.
Comment: Thanks for the reply - that didn't seem to work, same error.  I then tried setting all "YES" values above to "NO", and the best result I could achieve is the movie just doesn't play.

MPMoviePlayerController Stack Overflow


What is my crontab -e local file path? I want to set it via BASH script

Question: In my Ubuntu, my username is "meuser". When i do crontab -e, i can setup my rules. But instead of doing it with crontab -e, how can i do it directly to a file? Which file i cant modify?
Answer: Quoting crontab's man page:

There    is    one   file   for   each   user's   crontab   under the
         /var/spool/cron/crontabs directory. Users are not allowed to  edit  the
         files  under  that directory directly to ensure that only users allowed
         by  the  system  to  run  periodic  tasks  can  add  them,   and   only
         syntactically correct crontabs will be written there.  This is enforced
         by having  the  directory  writable  only  by  the  crontab  group  and
         configuring  crontab  command with the setgid bid set for that specific
         group.

So you can't directly edit this file in a script (without sudoing around the restrictions). But, what you can do is the following: Just create a crontab file somewhere in the filesystem and then use
crontab <filename>

to install it.
Answer: You need to type in sudo crontab -e in the command line. The in the editor that pops open, hit the i key to insert in the cron that you want to add. I had to do this for my feedafever.com installation on jamescampbell.us/fever and it worked great running it from my ubuntu server instance on amazon ec2.


Where is some os logs in Debian 12

Question: It seems that some of the system log files (/var/log/syslog, /var/log/auth.log, /var/log/kern.log, ...) have been removed in the latest version of Debian, Debian Bookworm. What should be done to access these logs? Has the way they are stored and viewed changed?
Answer: In Debian 12, the traditional syslog system has been replaced with systemd-journald. This means that the old log files like syslog, messages, auth.log are no longer used. Instead, all system logs are now stored in a centralized journal, which is accessible using the journalctl command.
To view the system logs, you can use the following command:
journalctl

This will display all of the logs in the journal. You can also filter the logs by using options like -p (priority) and -u (unit). For example, to view only the logs from the syslog unit, you would use the following command:
journalctl -u syslog

You can also specify a start and end time for the logs you want to view. For example, to view the logs from the past hour, you would use the following command:
journalctl --since "1 hour ago"

Answer: You can also install rsyslog and then enable the logs again, by modifying the rsyslog configuration.
When you install the rsyslog package using apt-get there is already default configuration in place for the log files you require.
This is what's in my /etc/rsyslog.conf, and i didn't change anything
auth,authpriv.*                 /var/log/auth.log
cron.*                          -/var/log/cron.log
kern.*                          -/var/log/kern.log
mail.*                          -/var/log/mail.log
user.*                          -/var/log/user.log
#
# Emergencies are sent to everybody logged in.

Where is some os logs in Debian 12


Sequence number in AODV

Question: How does the sequence number at the destination node change? Does it become max of seq of RREQ in its current sequence number, or does the dst node increment sequence number by one? Please give an example!!
Comment: Is this homework? (We don't do homework.) If not homework, then you'll have to give us more details (eg, what devices make/model/etc) This stack likes to focus on answering specific problems . . .
Comment: Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
Answer: It is spelled out in RFC 3561:

6.1. Maintaining Sequence Numbers
Every route table entry at every node MUST include the latest
  information available about the sequence number for the IP address of
  the destination node for which the route table entry is maintained.
  This sequence number is called the "destination sequence number". It
  is updated whenever a node receives new (i.e., not stale) information
  about the sequence number from RREQ, RREP, or RERR messages that may
  be received related to that destination.  AODV depends on each node
  in the network to own and maintain its destination sequence number to
  guarantee the loop-freedom of all routes towards that node. A
  destination node increments its own sequence number in two
  circumstances:

Immediately before a node originates a route discovery, it MUST
    increment its own sequence number.  This prevents conflicts with
    previously established reverse routes towards the originator of a
    RREQ.
Immediately before a destination node originates a RREP in
    response to a RREQ, it MUST update its own sequence number to the
    maximum of its current sequence number and the destination
    sequence number in the RREQ packet.

When the destination increments its sequence number, it MUST do so
  by treating the sequence number value as if it were an unsigned
  number. To accomplish sequence number rollover, if the sequence
  number has already been assigned to be the largest possible number
  representable as a 32-bit unsigned integer (i.e., 4294967295), then
  when it is incremented it will then have a value of zero (0). On
  the other hand, if the sequence number currently has the value
  2147483647, which is the largest possible positive integer if 2's
  complement arithmetic is in use with 32-bit integers, the next
  value will be 2147483648, which is the most negative possible
  integer in the same numbering system. The representation of
  negative numbers is not relevant to the increment of AODV sequence
  numbers.  This is in contrast to the manner in which the result of
  comparing two AODV sequence numbers is to be treated (see below).
In order to ascertain that information about a destination is not
  stale, the node compares its current numerical value for the sequence
  number with that obtained from the incoming AODV message. This
  comparison MUST be done using signed 32-bit arithmetic, this is
  necessary to accomplish sequence number rollover. If the result of
  subtracting the currently stored sequence number from the value of
  the incoming sequence number is less than zero, then the information
  related to that destination in the AODV message MUST be discarded,
  since that information is stale compared to the node's currently
  stored information.
The only other circumstance in which a node may change the
  destination sequence number in one of its route table entries is in
  response to a lost or expired link to the next hop towards that
  destination.  The node determines which destinations use a particular
  next hop by consulting its routing table. In this case, for each
  destination that uses the next hop, the node increments the sequence
  number and marks the route as invalid (see also sections 6.11, 6.12).
  Whenever any fresh enough (i.e., containing a sequence number at
  least equal to the recorded sequence number) routing information for
  an affected destination is received by a node that has marked that
  route table entry as invalid, the node SHOULD update its route table
  information according to the information contained in the update. A
  node may change the sequence number in the routing table entry of a
  destination only if:

it is itself the destination node, and offers a new route to
    itself, or
it receives an AODV message with new information about the
    sequence number for a destination node, or
the path towards the destination node expires or breaks.
Comment: Hi....I am not able to clearly understand the the section:6.6.1. Route Reply Generation by the Destination

   If the generating node is the destination itself, it MUST increment
   its own sequence number by one if the sequence number in the RREQ
   packet is equal to that incremented value.  Otherwise, the
   destination does not change its sequence number before generating the RREP message.
Comment: OK. My point is that you should go to the source for your answer. Just understand that AODV is an experimental protocol. It will get a standards-based RFC if it goes mainstream, but, for now, it is marked as experimental. That means that everybody is free to make a different version with different ways of doing things.

Sequence number in AODV


How are private keys handed to users in Identity-based Encryption?

Question: I'm using IBE in my applied-crypto project in primitive form. I saw many articles about IBE, but didn't find how user can get private key is generated by PKG after EXTRACT method.
So, my question: What is the best practice to hand private key to user after EXTRACT method?
Answer: Crypto is nice and clean until you think about how to manage the keys. Common Identity-based Encryption (IBE) schemes have a tremendous disadvantage, that a trusted key authority generates private keys for some user and the user has to be given that key. The most common scenario for IBE is a corporate environment, so I will only ways to solve that in that environment. Note that all communication should be TLS encrypted.

If the user registers, they get an e-mail account and a private key that has that e-mail account as an identity. The security games in IBE schemes usually consider that an attacker can register many e-mail accounts and therefore request many the private keys with those. The schemes are proven secure when the attacker cannot derive the private key of an identity of another user.
This works fine, but the user would have to handle the key themselves and might even inadvertently misplace or leak it.
In a corporate environment, we usually have an IT department which either sets up the corporate workstation or adds a secure container on a BYOD-device. This administrator surely can write the private key for that user to a USB key and copy it to the configuration of the software that uses it. This makes it slightly harder for the user to do something dumb. Keep in mind that the private key can always be regenerated based on the e-mail account.
Other hardware is also possible. An administrator could generate the private key and push it to a smartcard which is then given to the user in person.
This has the added bonus that the user cannot really copy their privileges, because smartcards usually have a hardware-enforced copy-protection. They could still give their card to somebody else.

If the user abuses their privilege to access some data, be sure to have the necessary logs and a system in place to detect those events.
Answer: You can implement a Key Generation Center and a Key Distribution Center. You must define this like a Trusted Authority.
Hint: Send this key using HTTPS after a user request, if you you want a dynamic system. However you can send it to e-mail address and save to using it.
Comment: Can you go into more detail, what exactly the KGC and KDC are doing?
Comment: A Key Generation Center is used to generate the private key, while the KDC used to transmit the key to the user.
Comment: OK, but how? That's the question, isn't it?
Comment: You can use a Token to send the key.


How to find and remove unused class files from a project

Question: My XCode project has grown somewhat, and I know that there are class files in there which are no longer being used. Is there an easy way to find all of these and remove them?
Answer: If the class files just sit in your project without being part of a target, just click on the project itself in the tree view, so you see all files in the table. Make sure you see the "Target" column in the table view, iterate through your targets and find the files that don't have a check anywhere -> they are no longer compiled.
But if you still compile the classes and they are no longer used, that case is a bit more  difficult. Check out this project
http://www.karppinen.fi/analysistool/#dependency-graphs
You could create a dependency graph and try to find orphaned classes that way.
Edit: Link went dead, but there still seem to be projects of Objective-C dependency graphs around, for example https://github.com/nst/objc_dep
Comment: The target column may be misleading, in that it only considers the active target. If the class is not used in the active target but is used in another target, the target column will have no checkmark even though it is being used.
Comment: That's why I suggested to try to find files that don't have a check in any of the targets. Of course, this won't be much fun if you have a lot of targets..
Answer: if they are C or C++ symbols, then you can just let the linker do the work for you.
if you're looking to remove objc symbols, then try to refactor the class name (e.g. to rename the class), and preview the dependencies that it turns up. if you reference classes/selectors/etc. by strings then... it may not be so effective. unfortunately, you often have to also test manually, to verify that removing a class does not break anything. remember that resources (like xibs) may reference/load objc classes as well.
Answer: This is a tricky question due to how dynamic objective-c is as you can never guarantee that a class is not going to be used.
Consider if you generate a class name and a selector at run time and then look up that class, instantiate that class and then call a method on that newly created object using that newly created selector. No where in your code do you explicitly name and instantiate that object but you are able to use it anyways. You could get that class name and selector name from anywhere outside of your code, even from some data from a server some where. How would you ever know which class is not going to be used? Because of this there are no tools that are able to perform what you are requesting.
Answer: Searching the project with the class name might be an option, thought it may not be the best solution. Specially it might be time consuming when you have many classes.


@Override on Implementation

Question: Would you put the annotation in implementation class methods? Does it serve any purpose? If you mistype or don't have it, it is a compile error anyway.
Answer: While it's not required to use this annotation when overriding a method, it helps to prevent errors. If a method marked with @Override fails to correctly override a method in one of its superclasses, the compiler generates an error. Its better to fail fast, catch the error soon rather than later figure out you wrote hashcode() but you meant to write hashCode(). @Override helps in finding the problem sooner rather than later.
Similar questions on SO.

when-do-you-use-javas-override-annotation-and-why?
should-i-add-an-override-annotation-when-implementing-abstract-methods?

Also see this.
Answer: It's rather useful. If a method annotated with @Override doesn't really overrides method in a superclass you'll get a compilation error.
For example, if you have a class Foo and you create a method:
@Override
public boolean equals (Foo foo) { ... }

then you'll get compile-time error which will tell you that equals (Foo foo) doesn't override any method in Foo's superclass.
Modern IDEs (like IntelliJ) add this annotation automatically when you use some code-generation features of the IDE.
Comment: I think the equals(Object) vs equals(Blah) is the best example of how @Override can help prevent a major (but hard to detect) programmer error.
Answer: I assume you are asking about annotating methods which are defined in an implemented interface, or as abstract in a super class.  In that case, you are correct that a typo in the method signature will result in a compile error with or without @Override.  However, I think the annotation is still helpful to explicitly mark a method as implementing an interface.  If the interface ever changes, having @Override annotations on all the implementing methods can help pinpoint which method signatures have changed and need to be updated.
More importantly, as mklhmnn mentioned in his answer, if a method is removed from the interface, the @Override annotation in your implementing class will cause a compile error.  Without the annotation, you might not be aware that a method had been removed from the interface, which could lead to subtle bugs.
Answer: I don't use it and never had a problem. I don't know why suddenly everybody starts using it (Eclipse? which I don't use either).
Refactoring is not a problem, IDE checks that for you anyway.
@Override may help code readability though, so that it's clear to HUMANS what's going on, not compilers. Although my IDE will also mark override methods graphically, it is not very prominent, but the point remains, this is something tools can do for us automatically.
Answer: Marking a method as @Override will produce a compilation error if the API changes so no super method is available any more. Maybe that's the reason.
Answer: I think it's also nice to do this as an indication to yourself that the Javadoc is elsewhere, you didn't just forget it.

@Override on Implementation


What is the incentive for people who provide us ETH for testing?

Question: this is not a technical question, however I was curious to know what is the incentive for people who provide us ETH for testing? Thanks
Answer: Testing blockchains were created for testing purposes so the coins are worthless by design.
PoA networks like Rinkeby, Goerli, Kovan the funds were allocated to respectable members with the explicit purpose of giving away funds for other projects testing needs.
PoW networks like Ropsten anyone can mine, some people will mine for they own projects (software or hardware). Then give away the unused eth. Some miners are managed by the community for the explicit purpose of keep the network running.


List all music files on device cordova/phonegap

Question: I'm new to Cordova and I'm trying to build an app where I need to get all of the music files on the device. How would I go about finding them? I can use DirectoryReader to enter a direct path to the music folder, but I would like to automatically find it. Is this possible? Are there any examples that you know of?
Answer: well, you will have to read recursively all folders starting from root.
Read root folder. If object is folder- read its content. if object is file- check it if it's media file and add its path to list.


What does the term multiplexing mean in computer science?

Question: What does multiplexing mean (in it's abstract form)?  I understand you have 'multiplexers' in hardware and 'muxing' in networks.  What would a good high-level definition be?
Comment: nah.  I'm studying for an exam.
Answer: Since the definition is basically 'the doing of multiple things at the same time' or 'interleaving of many things'. I would suggest it's as simple as that when applied to computer science.
Though are are specific instances of multiplexers such as putting multiple signals through a data channel, other words in computer science may also be used to replace multiplexer. For example you could consider the running of many processes as multiplexing but the more common term is multiprocessing.
However the hardware/software example of many signals over a wire/channel is the canonical example for me.
There's a nice definition here - .../wiki/multiplex.
Answer: Multiplexing, in computer networking, refers to a technique whereby multiple users share the bandwidth of a channel. You could use the analogy of a postal service, whereby different people(senders/transmitters) use one postal office (the channel/ medium) to send letters to their loved ones (receivers).
Two famous forms of multiplexing are Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM). TDM is whereby the channel regulates the senders such that only one sender can send a message at any one time using the networks full capacity/ bandwidth. After some time interval, the next sender can send, and this process repeats for all senders. Therefore in our analogy, the Sender A has one hour to send letters, and the postal service personell will use their full resources to deliver the letters to their respective recipients. In FDM, all senders can use the network bandwidth the whole time, but will be limited because there are multiple users at the same time and therefore delivery could take a little longer. Back to our analogy, Sender A sends sends a letter but the post office has other letters as well from other senders, therefore the delivery will take longer.
Depending on how you see it, either of them could be faster than the other. But like I said before, there are other types of multiplexing as well so it is not confined to the two ways I described above. I hope this makes sense to you.
Answer: Multiplexing is a process to combine multiple signal for transmit it over a single channel.multiplexing is sending multiple signal or stream of information on a carrier at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving ends..


Pretend a structure to write guides?

Question: I am creating a website, where users are able to create guides for a video game. Since there is/could be a strict structure for the writing of the guide, I am not really sure if I actually should pretend a structure for the sections that should be filled out. Should I rather make a link where the recommended  structure of a guide is shown and let the user eventually do what he wants to do, or shall I actually pretend a structure for the user so the guide follows a certain quality line?
Comment: Would your users - those who read the guides - be annoyed or disturbed if the guides do not follow a consistent style? Or is that something they would consider to be normal - and something they like about your site?
Comment: Hm that's a good question. I think it would be better to follow a strict guideline so you have a chronological sequence. Readers would always know where what to read
Comment: It's good if you create a structure so that the player, when he sees the walkthrough knows exactly which part he needs to look for. So mainly sections could do very well.
Answer: Since you're talking about a competitor to GameFAQs, you should be looking at their model in great depth.
As I reminisce about when GameFAQs actually started (I do actually remember finding it in the original Yahoo! listing, back when the engine was moderated by real people), the number of guides I've used there, and the few guides I've written for it -- the site would be a strong case for not restricting structure. The site has existed largely untouched for a long time!
The success in its simplicity is similar to Craig's List's continued popularity. It isn't necessarily pretty, but I can very easily get the information I'm looking for and get out.
Street Fighter does not demand the same structure as Final Fantasy, or as Mass Effect, or another genre. Even within genre, different types of guides do better in different formats. Is this guide a walkthrough, a super-move cheat sheet, or is it about solving the complex mini-games within the larger gameplay? Different scenarios will not fit the same style.
You are also trying to create a site that is driven by community contributions... at least, I'm assuming you're not sending your users a check when write a guide. So, as an author, if I want to contribute something and you put too many restrictions on my "creative genius" I'll probably just go somewhere else (GameFAQs, probably).
Comment: While I agree, providing optional templates with placeholder data/elements could increase the quality/display of user contributed guides/tips.
Comment: Alright man thank you very much for your suggestions :) I think I will use optional templates and will reference style guides on how to write the guide but mostly will let the user do what he wants to do :) But one more question: I am writing my database model now and I have to think about character limitations. Should there be character limitations, because I imagine trolls could post endless texts and that wouldn't be cool.. How should one handle that?

Pretend a structure to write guides?


How to save an object graph with EntityFramework, lazy load disabled, proxy disabled and entities are non trackable

Question: Here is the situation I am into using EF.

Repository gets an instance of A and returns to the presentation tier (i.e. MVC controllers)
The controllers change certain properties on A's instance and the given it back to persist.
Before persisting, I need to figure out what change was done to the object and validate if the change is permitted or not.
To compare the change, I need the old instance from the database.
But EF returns the same dirtied instance, so I cannot compare them.

What I tried doing:
Class Structure
public Class A {
 public B B {get;set;}
}

public class B {
  public ICollection As {get;set;}
  public C c { get; set;}
}
public class C {
}

B and C map to the same database table.

Though it's because EF is tracking the old instance and since save has yet been called on the instance, so it's returning back the same inatce.
So I turned off lazy loading, proxy gen, and return the objects as non-trackable for the repository.
Now EF returns fresh record from the DB, but If changed some property on A, then in the B's collection of A, it loads only the instance of A that I changed, not the entire collection.
When If I want to create a new A and save, I do the following
B b = GetSomeOldB();
A a = new A();
a.B = b
a.Save();
So I essentially I add the new A to the context and call SaveChanges.
Ef returns and exception that "Unable to cast C to B".

Basically, all I want is to get the old object graph from the context when I ask for, compare with the dirtied one the giving the dirtied to persist.
Would really appreciate any help!!
Here is the solution that finally implemented:
1. Turned back on the Tracking and proxy creation
2. Get the orginal copy from EF.
3. Wrote this generic method to hydrate a new instance of the entity
public ICollection<T> GetOriginalCollection<T>(ICollection<T> changedCollection) where T : class {
      ICollection<T> original = new Collection<T>();
      foreach (var item in changedCollection) {
          //Dont return the newly added ones to the original collection
          if (_context.Entry(item).State != EntityState.Added){
              original.Add(GetOriginal(item));
          }
      }
      return original;
  }

public T GetOriginal<T>(T changedEntity) where T : class {
      Func<DbPropertyValues, Type, object> getOriginal = null;
      getOriginal = (originalValues, type) =>
      {
          object original = Activator.CreateInstance(type, true);
          foreach (var ptyName in originalValues.PropertyNames) {
              var property = type.GetProperty(ptyName);
              object value = originalValues[ptyName];
              //nested complex object
              if (value is DbPropertyValues) {
                  property.SetValue(original, getOriginal(value as DbPropertyValues, property.PropertyType));
              } else{
                  property.SetValue(original, value);
              }
          }
          return original;
      };
      return (T)getOriginal(_context.Entry(changedEntity).OriginalValues, typeof(T));
  }

Comment: Take a look at [breeze.js](http://www.breezejs.com/). You'll instantly fall in love :)
Answer: I think what you want is working in disconnected environment. You can attach disconnected entities and provide what changed in the graph by specifying its EntityState. If you want you can create Interface like IObjectState and implement in your models to find out what exactly changed in the graph.
Comment: Thanks @Krishna. This is how fixed it. Turned the AutoDetection back to on and the proxy creation and get the original copy when needed from EF. I've the code snippets
Comment: You should also implement an IsRowVersion field in anticipation of concurrency conflicts.


Approval Process - Prevent submitter from approving

Question: Is there any way we can prevent submitter of approval process from approving the record?
Answer: There could be situations where submitter and approver are part of the same queue where anyone of them can approve the record.
To restrict, submitter to approve the request follow this steps:

Create two text fields to capture submitter and approver's id.
Create field update from approval processes to update those field values during submission and approval.
And, create an before update trigger on that object which will verify if approver's Id is same as submitter's id and throw the error.
Also, other than trigger, you can use validation rule which will prevent approver's Id same as submitter.
Comment: Thanks Santanu! How do i capture submitter and approver's id in workflow action in Knowledge Article object?
Comment: Loggedin userid who is submitting or approving
Answer: Your approval process shouldn't be designed to have an approver same as a submitter, if you have such a situation then there is no sense of having an approval process in place!
There are many ways to select an approval:
Manager of Submitter
Upper Hierarchy User
Specific User etc
If you use the approver wisely then this shouldn't appear!
Another thing is if you are logged in as an admin then it might be able to submit & approve too! Try with users with non-admin profiles!
Trailhead Link for Approval Process: https://trailhead.salesforce.com/en/content/learn/projects/build-a-discount-approval-process/create-an-approval-process
Comment: Thanks Harting! For one of the steps, we are allowing to choose approver manually. Also in case of queues, it is possible to have submitter and approver as same person. Can we somehow stop selecting submitter as approver by any validation rule etc.?


Close vs. Ask vs. Open

Question: In after hours trading, if I wanted to buy a stock and the closing price was $3.00, the Ask price was $3.50 and the Open is $3.75. What would be the price of the stock when purchased after the closing bell?
Answer: If the current ask is $3.50, you would buy that one.
Answer: Applicable to trading in the US:
The opening price has nothing to do with any orders placed later in the day.
The short answer is that if the size of your "limit" order is less than or equal to the available size at $3.50 then you'll be filled at $3.50 (maybe).
Unfortunately, it's not always that simple.
If the size of your limit order is larger than the ask volume at $3.50 then you'll get a partial fill unless someone else comes in to sell you the balance at $3.50
If you place a "market" order to buy and the market size at $3.50 is less than the size of your order then you'll get a partial fill at $3.50 and more shares at a higher price.
After hours trading is a different beast for illiquid stocks.  Sometimes you can hit the bid or the ask and the quote will disappear with no fill.  Cancel the order and the quote will reappear. Place the order again and the quote fades.
Coincidentally, this happened to me at 16:00:08 today after quick price bump 15 seconds before the closing bell.  I couldn't get the order in fast enough. The only way around it is with Level II and route directly to the  exchange offering the shares. I don't have Level II since this doesn't happen frequently enough to warrant the cost.  This example most likely doesn't apply to your proposed  trade because it's highly likely that with a 50 cent B/A spread, there would be many traders happy to  fill at that price.

Close vs. Ask vs. Open


How can I share AppStore 1Password Pro on my MacBook?

Question: The information on 1Password regarding using/sharing the application one purchased in AppStore is that it is possible. You are given a rundown on how to install on your other device. But it doesn't work because the menus that are mentioned don't exist in the Mac version.
Originally I bought the 1Password Pro App on my iPhone (7) and would like to synchronise the password information via Dropbox on my MacBook Pro. I never received a licence nor secret code by e-mail.
Is there someone who had/has this same problem? When replying please keep it simple as I'm not a computer genius
Comment: Mac App Store is different from the Mobile App Store. Contact 1password support.
Comment: Which instructions (link) are you following here? Basically you need to get the application from the Mac App Store and then connect to the same Dropbox as you did from the iOS version.
Answer: If your ultimate aim is to have access to 1Password and all your stored passwords, serial numbers, etc on both your iPhone and your Mac, you need to install 1Password on both devices.
Assuming you've done that, you have a number of options, but since you're wanting to use Dropbox then do as follows:
On your iPhone
Make sure you have synced your 1Password data to Dropbox. To do this:

Launch 1Password on your iPhone
Tap on the Settings icon at bottom right
Go to Vaults > Primary > Sync Service
Tap on Sync with Dropbox
Follow the prompts to finish the process

On your MacBook
Do as follows:

Start from scratch and install 1Password on your MacBook again (i.e. If it's already installed, delete it and then download/install it again)
Launch 1Password
Now, when it launches the first time you should see a screen similar to the one below:

Select the Sync using Dropbox option
Click on the Choose File... button
Navigate to Dropbox and select the 1Password data file (it'll have either a .agilekeychain or .opvault file extension)
Follow the prompts to finish the process

NOTES:

As mentioned above there are a number of ways you can sync data between iOS and macOS. If you still have problems, you may want to investigate other options (e.g. WLAN, iCloud, etc).
The AgileBits Support Forum is actively staffed, so it's a good place to go to seek direct support.


Configuring a VMDG280 router to point to an internal web server

Question: I have a netgear VMDG280 router.  I have a static IP address.  Anyone know how I can configure this router so if I type in my IP address, it shows me the same apache ready webpage as I get when I go to localhost from the browser?
Answer: Port forwarding is correct, as @Joe pointed out.  Here is a link to a help page for your router model.  The section you are looking for is...

Name:  Whatever you want
Start Port:  Probably 80, unless you want to have to append a <code>:1580</code> or something to the URL.
End Port:  Whatever your Apache server is listening on... again, probably 80 unless you changed it.
Protocol:  Both is fine
Local IP Address:  IP of the machine your Apache server is running on.
Comment: It depends on the variety of data being transmitted.  Different higher level protocols are designed to use one, the other, or both.  TCP is used when reliability is the top concern, i.e., the receiver acknowledges receipt of every packet, and the sender waits for that acknowledgement before continuing.  UDP is used when speed is the top concern, i.e., no acknowledgments.  [Here](http://www.skullbox.net/tcpudp.php) is a nice explanation of the two in comparison.
Comment: I understand that you've said to use `Both` for the protocol option, but when would it be appropriate to use TCP or UDP?
Answer: You need to forward the port on your router over to the machine with apache installed.
Not knowing the router myself I can only say you will need to direct traffic on port 80 hitting the router to point to the IP address you have assigned to your machine inside your subnet.
A really helpful guide, I find, is at http://portforward.com/help/portforwarding.htm


Survival analysis: informative right censored data question

Question: I am attempting to analyze data for someone and am getting stuck on finding something that is appropriate. The design of the experiment is as follows: vials are set up with 10 flies  per vial (either mutant or control flies). Flies are tapped to the bottom of the vial and the time it takes half the flies to reach a certain height is recorded. Unfortunately, the observer watched for 90 seconds and if half the flies had not reached the designated height by this time the data was recorded as >90. My first thought was to use survival analysis since it can handle censoring. However, if I understand correctly, these right censored data would be considered informative, since flies that did not reach the height by 90 seconds are obviously slower, and might, in fact, never reach the designated height. This could also correlate with the level of the predictor (mutant vs. control). From my understanding a standard survival analysis would not be appropriate here. I have two questions:

Is my understanding of informative right censoring correct?
If so, does anyone have any suggestions for how I could analyze this dataset? Obviously one solution would be to have the observer continue watching for longer, but, aside from the fact that much of the data has already been collected, I'm also not sure it would solve the problem because the flies may be so impaired that they never reach the designated point.
Thank you for reading and I appreciate any input!
Answer:
No. The condition for noninformative right censoring is that, among vials that reach 90s without half the flies getting to the desired height, whether observation continues or stops is independent of how much longer the flies would take.  This is true: according to what you say, observation always stops at 90s

Survival analysis is one sensible approach.


How to remove gnome settings from ubuntu 20.04 with unity desktop?

Question: I have ubuntu 20.04 with unity desktop. I removed the existing gnome shell and now when I search for settings I have two of them one is the system settings and the other is the gnome settings. How can I remove the gnome settings from ubuntu 20.04
Comment: try "sudo apt remove gnome-control-center"
Answer: After you've install Unity Desktop and, logged into it, use:
sudo apt remove ubuntu-gnome-desktop
sudo apt remove gnome-shell

This works for for Ubuntu 16.04 to 20.04 and even 20.10 (Groovy). Source:

Ubuntu – How to remove Gnome Desktop Environment without messing Unity DE? (Ubuntu 16.04)

Although article is written for Ubuntu 16.04, you can verify the package is still around for 20.04 (called Focal) by visiting Package: ubuntu-gnome-desktop:

Personally I use Unity all the time but like to keep both desktops installed. Occasionally I need to answer other users' questions about Gnome Desktop.

Note: ubuntu-gnome-desktop might not be installed
Because it is a transitional package since 18.04 these instructions from:

Why and How to Install Unity 7 Desktop on Ubuntu 18.04 LTS

Tell you to simply use:
sudo apt remove gnome-shell

The article doesn't mention ubuntu-gnome-desktop needing to be removed. This article includes additional tips on setting up Unity Desktop.
Comment: Should probably also add a "sudo apt autoremove" to remove all automatically installed packages of these desktop environments? Only then, gnome-settings may be effectively removed.
Comment: @vanadium The link discusses that plus at lot more. I debated myself how much of the link to include. Perhaps you wouldn't mind visiting the link and giving me your thoughts on amount of details to include in my answer?
Comment: Policy of this site is to include all relevant stuff, so the anwer is self containing. Anyway, the link probably is not anymore up to date: `ubuntu-gnome-desktop` currently is a transitional package that is not even installed by default.
Comment: @vanadium You are correct it has been transitional package since **Ubuntu 18.04** and I've revised answer to reflect that. I appreciate your input.


What do my children do when I tell them to do their chores?

Question: I'm just curious what my skyrim children are doing when I tell them to do chores. They knock stuff over in the house sometimes but they don't clean it so what are they up to?
Answer: They will wish the floor. Child labour!

"Go do your chores, (Name)." — You can ask your child to do chores; they will begin to sweep the floor unwillingly.

I experienced back talking from some children, this just happens. In the case of back talk, they won't do anything.
Knocking things is, as @Ben mentioned, a poor collision detection.
Source:
http://www.uesp.net/wiki/Skyrim:Adoption
Answer: When you tell them to do chores, and al is activated which allows them to sweep the floors until you tell them to do something else such as go to bed or go play outside. running over stuff is just a collision problem.


Why would I use lntg:selectSObject?

Question: The Lightning Component Developer Guide reference includes the event lntg:selectSObject. Per the docs, this event:

Sends the recordId of an object when it's selected in the UI.

However, the sample code doesn't really help me understand when or why I would use this standard event. Does it cause some sort of interaction with SF1/LEX? Does it mark the record as recently viewed (like FOR VIEW)? Is it just a helpful standard event that all my components can expect?
Comment: Did you try to ask Salesforce support about that?
Answer: I just found this description of the events on org62 from PM Eric Jacobson:

ltng:selectSObject is perfect for building master/detail components where you display a list of records and then want another component to display the selected record.
ltng:sendMessage is a general purpose event that dispatches a string message.
Both of these events have an optional "channel" attribute - this is a string that can be used to "tune" your component instances into each other - for example, if you want to put multiple master/detail components onto a page, you can set them to separate channels so that they won't conflict with each other.

Eric also clarified that there are no "standard" platform components listening for these events, these are just useful building blocks for developers. That said, there may be AppExchange components that use them / listen for them.
Answer: It is an event much like the ltng:sendMessage. It's main purpose is to tell OTHER components that a record was selected on your component.
For example: let's say you have a calendar app. For that you have a component that creates events and a custom component that finds users based on filters. Once you selected a user, you can use the lntg:selectSObject event to tell the other two components wich user will receive the new events and what events to show on the calendar.

Why would I use lntg:selectSObject?


Strong Wind(s) or High Wind(s)?

Question: Which one is more popular?
I always used strong wind, but I found high winds also used some times.
Answer: The terms strong winds and high winds are synonymous in everyday jargon, although they may have different meanings to a meteorologist.
As far as what phrase is more popular, I imagine it varies by locale. You can use Google Trends to analyze the popularity of two competing search terms. Here are the results for strong winds and high winds:

Worldwide, the two terms are used about as often, although high winds is a slightly more popular search term.

In the US, high winds is decidedly more popular than strong winds. This difference is most pronounced in North Dakota, Hawaii, and Nevada, where high winds trounces strong winds.

In other countries, such as New Zealand, Canada, and Australia, the term strong winds is quite a bit more popular a search term than high winds.

Some countries have virtually no one searching on the term high winds. The Philippines, Singapore, Finland, and Sweden are four such examples.

In a nutshell, both terms are valid, but which one is more popular depends on the region.
Answer: The CORPUS OF CONTEMPORARY AMERICAN ENGLISH indicates that high winds is used more than strong winds (435 vs 251 occurrences).
Answer: Either one is fine, although you do see "strong" used more. But it's your pleasure. Paul Simon repeats the phrase "strong wind" on his album Graceland. But the National Weather Service says on one of its pages "This information is most useful in the decision-making process to decide which people might be most vulnerable to high winds at inland locations."

Strong Wind(s) or High Wind(s)?


How do I make sure my notes and highlights from Google Play Books are saved when I factory reset my Android phone?

Question: I need to unlock my Samsung Galaxy S3 Mini, Android ver. 4.2.2, and I'm not sure if the notes I took on my books using the Play Books app will still be there after the reset. I need all those notes for school and it would take forever to copy them all down.
Answer: You can check from your PC on this address that all your notes and highlights from Google Play Books are saved in the cloud and not in your device:
https://play.google.com/books/


Using PHP to connect to Microsoft Office 365's Exchange Online services

Question: The company that I work for has migrated their local exchange to a hosted Office 365 solution. We are in the process of building out several externally(to our local network) hosted websites and would like to use PHP authentication to build upon our existing, hosted user base.
Can anyone explain or point to some documentation of a way to use PHP to connect to a remotely hosted AD (in this case Office 365) and authenticate users to it and also how to get access to the calendar events of the logged in user
Thank you for your time and effort.
Answer: You can use PHP's LDAP functions just as you would for a self-hosted Active Directory Server.
Microsoft has some information on this themselves:
    Web Single Sign-On with PHP and Windows Azure Active Directory


How to investigate (and get control over) the execution order of 3 Rules working on the same action?

Question: I have three Rules to do something after saving content. I need to know which one is executed first and how I can control this order?
Is there a certain answer for this question?
Answer: It's based on the weight. Edit the  Rule settings and you'll find a drop down to set the weight. I believe those with a lighter weight, e.g. -1, are  executed before those with heavier weight, e.g. 5.
Comment: to "view" what is happening, on each rule add an action "display a system message". e.g. on rule with weight -1 say "on rule number 1, weight -1", when you are done, delete the messages.
Answer: You can set a weight for each rule.
Answer: Something that will help you find the answer to your question, is to have a look at Rules debugging ... Within the Rules settings, experiment a bit with the debugging facilities that come with the rules module. At least have a look at the "Rules Evaluation Log" (to check that the Rules logic being executed, actually matches what you expect that logic to be).
Depending on what the result of that type of debugging is, you may also want to (temporary) enable the Devel module, so that you can (temorary) add a Rules Action like "Display a value" (in your case of the entire node/webform that's used to submit that attached file).
For way more details about these 2 variations, refer to Rules debugging, as explained in the answer to "How can I display the value of a variable inside a condition?".
To actually control the order of execution of 3 rules, you may want to implement these 3 rules as Rules Components, and then build a 4th rule in which the Rules action is to execute these 3 rules components ... in the exact order that "you" want them to be executed.


principle component analysis: help with interpretation

Question: I'm teaching PCA to myself for some environmental data analysis. I understand the intuitive and geometric definition, but I'm not quite sure what exactly it's telling me. What exactly do the eigenvectors say about variance (and of which numbers)? What exactly should I be looking for if I'm interested in the variables most closely related? My intuition is telling me to find the smallest Eigenvector and then look at the eigenvalues in that row to find values with an absolute value greater than .5. Cheers!
Answer: PCA is just a change in the representation base (i.e. vectors used to represent your data). By checking the eigenvalues you can have an idea about the importance of each original vector on building the new representation base. This means that some "features" in the original representation are more important that others for data discrimination.


Having Trouble Replicating WordPress IE Cross-Browser Issue

Question: I've been having an issue with a client's site that I haven't been able to replicate. A few users have reported an issue with the website (http://beyondbbd.com) where the pages don't display a majority of the styling and render as below:

In trying to troubleshoot, I am having difficulty replicating the issue on my browser checking system (Browserstack), or finding an underlying cause.
Users reporting the issue are using Windows 7 and Internet explorer (though I don't know their version of IE at this time), and are encountering the issue on these pages, among others:
http://beyondbbd.com/motivational-speakers-for-business/
http://beyondbbd.com/leadership-workshops/
http://beyondbbd.com/internal-coach-training-program/
I haven't been able to replicate on any version of Windows or IE using Browserstack, but this issue has been reported by more than one user so I don't think it's an isolated case.
Anyone have any ideas as to what the cause could be, or how I could replicate the bug?
Thanks in advance!
-Nick
Answer: I couldn't replicate, but you have two opening 'head' tags as well as lots of other validation errors (stray closing tags). It is possible that this is chocking some instances of IE.


I heard professional chessplayers must train physically as well as mentally. Why is that?

Question: I heard that both Fischer and Karpov felt that physical training was extremely important to their success and that the Russian coaches also felt a certain amount of physical training was necessary.  Why is that?  How is it supposed to help?  What sort of exercise is supposed to help.
Comment: Because a chess game could take 5 hours. World champions need to be fit and stable not to blunder in the late game. You also need to be strong to play consistently throughout a tournament or a match.
Comment: So is aerobics what's important or strength training? or both?
Answer: You've heard it right. Physical training is as important as mental training in chess. Thinking is an energy intensive activity and often has a direct effect on the physical body.
Quoting this scientific american article by By Ferris Jabr on July 18, 2012, brain weighs about 1.4 kilograms, only 2 percent of total body weight, it demands 20 percent of our resting metabolic rate (RMR)—the total amount of energy our bodies expend in one very lazy day of no activity.
Karpov had lost 10kg (22lb) over the course of 1984-85 Kasparov-Karpov world championship match. Quoting Kasparov from this interview, I pay a lot of attention to my physical condition; to be fit under the terrible pressure of big competitions. Obviously this is becoming more important with age.
From a study by Speakman JR et. al , being physically fit improves resting metabolic rate (RMR) which is a major contributor to daily energy reserve and thus any increases in RMR in response to exercise interventions are potentially of great importance.
Chess, as you know is a brain intensive activity and thus RMR plays an important important role. Therefore from the 1st and the 3rd paragraphs, it is clear that physical fitness improves mental fitness and therefore beneficial to chess.
Comment: It doesn't explain how some top players are obese (I won't name names), old (Smyslov, Korchnoi), alcoholic (for awhile, anyway), or just weak physically (Tal).
Comment: @JeffLowery Smyslov, a world champion, and Korchnoi, a challenger to Karpov, were top players before they got old. Tal wasn't weak physically until he was suffering from kidney problems.
Comment: @JeffLowery Overweight top players are rare these days.  The main problem that obesity causes is poor glycogen and insulin regulation, which affects concentration over long periods. This is essentially _cognitive stamina_.  Fit players can concentrate as well after 6 hours of play as they do after 5 minutes of play. Carlsen is famous for the evenness of the quality of his play.  This doesn't mean that less fitness-conscious players cannot play very well; they will just tend to be outperformed by fit players over long periods, all other things being equal, which typically means in the endgame.
Comment: @HerbWolfe My point is that they were top players in their sixties. Not quite as good as they once were, but still in the top 20.
Comment: Kasparov always included soccer in his summer training camp.  Carlsen plays soccer.


Licensing using openWRT opkg

Question: We are planning to use openWRT "Attitude Adjustment" for out development. We have some software which we need to commercially license ; Is it possible to use opkg to license them commercially ? Is there any document which tells me licensing policies of opkg with respect to commercial code ? Thanks.
Answer: yes you can use the Attitude Adjustment buildroot and combine it with OpenWRT packages that have a different licence than the GPL.
The important part is that you have to release a GPL tarball to all the GPL stuff that you are using and evertually you have modified. The proprietary part can be released in binary form, if it is a package that is totally independent from previous sources.
I will make an example. Ubiquiti releases a firmware for its devices that is OpenWRT based. Ubiquiti releases a GPL tarball that contains the source code of everything that was GPL and inherited from OpenWRT. The binary blobs of software developed from scratch by ubiquiti are not released as source code.
Answer: it's GPL
so i guess it's a bad news for you.
You can always contact the author/s to see if they want to change their license.

Licensing using openWRT opkg


Understanding derivative as slope to the curve

Question: I am a novice in calculus and have been learning differentiation lately. I read many books and saw you tube videos. There I noticed that to find the slope of a point in a curve,people take a point $P=(x+h,f(x+h))$ and determine the slope $\frac{f(x+h)-f(x)}{h}$. Now to find the slope more accurately, they take the point $P$ close to $(x,h)$ and say that it boils down to a tangent line. But the tangent by definition will intersect the curve at only one point,in that case shouldn't $h=0$? I know that gives indeterminate form and the people use limits by taking $h$ close to $0$. My question is how is that line a tangent? Even if it is close to $0$,it is still not a $0$,right? So that line still intersects. In that case isn't the derivative an approximation instead of an exact answer. I may be wrong,so please forgive me if I made any mistake.
Comment: You are right when you say that the true tangent would correspond to $h=0$. All values of $h$ which are close but not equal to zero, on the other hand, yield a curve which is only close to the tangent in the vicinity of the point of differentiation. And it might intersect the curve in one or more points.
Taking the limit $h\to0$ allows to compute the slope of the true tangent, while, as you say, computing the slope directly for $h=0$ would give a $0/0$ indeterminate form.
Comment: As @popoolmica indicated, you should understand limits in order to understand derivatives
Comment: I mean I know that it means what f(x) approaches when x is close to that value,but as I mentioned that tangent is a not real tangent,is it right?
Comment: Maybe your confusion comes from the idea of an intersecting line that, so to say, "becomes" a tangent ( which is impossible, as you noted). The tangent is not the final state of this line when h is equal to O, but the " limiting position" ( as is ordinarily said) of the intersecting line. This line never reaches this limiting position, but it actually tends to it. So this limiting position actually exists ( and is, as I said, the tangent to the curve).
Answer: Relevant answer I wrote on PSE
The simple answer is that you are making the 'h' exactly to zero, you are going to down a chain of decreasing the size of the quantity till you can approximate the slope of tangent line.
Here is a simple exercise to understand this:
Give me any number, I will give you a number less than it. For example, you give me $.1$ then I will say $.01$, if you give me $.001$ then I can give you $.00001$ .. so it an endless limiting process. And we can keep having this exchange till we reach the $h$ value where the rate of change of the function with the input is more or less the slope of tangent line.


How can you extract palladium from palladium chloride

Question: Hey guys I am working on a school project, focused on how precious metals can be recycled from industrial products. I am very much not an expert on the subject of chemistry. But I am just trying to get basic understanding on how to extract palladium from a catalyst like palladium chloride.
Thanks in advance,
Ilias
Comment: From what I have read, one good way to reduce Pd(II) to its metallic Pd(0) form is to "paint" the solution of Pd(II) onto a paper and heat in a reducing atmosphere of hydrogen. You should be able to recover the metallic palladium as a fine black powder. If you prefer, this can then be melted into a metal ingot.
Answer: Yes, there are several methods of reducing palladium chloride to elemental chloride.

By converting Pd(II) salt to palladium acetate ($\ce{[Pd(CH3CO2)2]3}$) and decomposing it at 200-300 $\pu{^\circ C}$. (link)

By using reducing agents

carbon monoxide
$$\ce{CO + PdCl2 + H2O → Pd + CO2 + 2HCl}$$
This is a qualitative reaction to determine the presence of carbon monoxide in the
air. A paper moistened with a solution of palladium chloride turns black in the presence of carbon monoxide due to the formation of finely dispersed metallic palladium. The reaction proceeds at r.t. The yield is high (84%).

Hydrogen
$$\ce{PdCl2 + H2 -> Pd + 2HCl}$$
Pd(II) salts can be reduced to finely divided elemental palladium by using
hydrogen. The reaction proceeds at r.t. but the reaction rate can be increased by
increasing the temperature. See this paper for more details.

Using $\ce{SnCl2}$

The reaction proceeds by formation of a complex. Yield is also high (90%). See here for more details.

Other reducing agents ($\ce{TiCl3, Fe, Cu, Zn}$)

Decomposition of palladium chloride. But the reaction is unreliable. The reaction proceeds at high temperature (590-740 $\pu{^\circ C}$). May release fumes of chlorine and hydrogen chloride which might be dangerous. Palladium obtained may be impure because of formation of various types of oxides. (link)

Decomposition of potassium tetra/hexachloropallade

Calcination in air. Dissolve the salt in a suitable solvent (usually water), "paint" the solution on a substrate, allow the solvent to evaporate and then start calcination. Pd(II) would become Pd(0), leaving a thin metal film on the substrate.

Binding of Pd-salt into an organic matrix (e.g., a zeolitic inorganic-organic polymer electrolyte), and then calcinate the product. However, using this approach, calcination should be done under vacuum or under an inert atmosphere (otherwise, oxygen might yield Pd oxide systems). In this case, Pd ends up as metal nanoparticles into a carbonaceous matrix.

Solution phase reduction. Impregnate silica with your metal salt solution, add a reducing agent like formic acid, ethylene glycol, $\ce{NaBH4}$ or hydrazine, heat at $\ce{150 ^\circ C}$ for ethylene glycol and at $\ce{80 ^\circ C}$  for the rest of the reducing agents, you will get Pd decorated $\ce{SiO2}$ particles. Nano particles are prone to oxidation at higher temperatures, so performing the reaction in inert atmosphere like $\ce{N2}$ or Argon will ensure the Pd(0) particles.

by Emeraldine base to form palladium nanoparticles. See here

Details about the points can be found in this researchgate article. But since this is a school project, points 3-7 are out of scope. The best method would be the "reduction through carbon monoxide".
Comment: Thank you very much for all the information!!
Comment: If this answered your question, please click the check mark so that the answer gets accepted. Thank you.


How to save slicer profiles?

Question: I've taken a bit of vacation and forgotten all the settings that I uncovered while tinkering with my printers.  Different settings for different printers for different materials.  I use Cura and PrusaSlicer, and they both behave more or less (randomly) the same.  Sometimes they save some things, most of the time they don't save the important stuff.  Neither slicer ever saves profiles, nor does it seem to have an option to, and they go weird if you change anything.
How are you supposed to save profiles?  Can I save them out to a file for later import when I need them?
I realize that both will probably have different ways to circumnavigate profiles, so I don't mind breaking it out into 2 questions if need be.
Me?  Oh I've just been hating profile saving for 12+0 years back when it was Slic3r.  At least with that software I could save them as a file and make sure that they were imported at the start of every single print.
An example of randomness: on this print on a large diameter printer, the infill speed was set to 4mm/s in Cura, making the print time 9 hours.  Once I fixed that, the print time was less than 2 hours.
Answer: Both Cura and PrusaSlicer save settings as comments in G-code files, so you should be able to recover settings form Gcode files, and save them as new profiles. I generally save projects along with G-code files, for extra security.

How to save slicer profiles?


Wick contraction with exponential operator in 2D CFT

Question: Consider a 2d CFT in radial quantization. Let $A(z)$ be some primary field and $Q$ a charge that can be written as $$Q = \oint dz \, z^{(h-1)}J(z)\tag{1}$$ for some holomorphic current $J(z)$. I will denote Wick contraction by an overline, as I don't know how to typeset it in mathjax. The question is: is it true that inside expectation values (which implicitly include radial ordering)
\begin{equation}
\langle A(z) \,:e^Q: \rangle \stackrel{?}{=} \langle \overline{A(z) Q}\, :e^Q:\rangle\tag{2}
\end{equation}
where $$ \overline{A(z)\, Q} = \oint dw\, w^{(h-1)}\overline{ A(z) J(w)},\tag{3}$$
and $\overline{ A(z) J(w)}$ is the singular part of the OPE between $A$ and $J$.
Here are some preliminary thoughts:
Suppose $h=1$ for simplicity. Expand the (normal-ordered) exponential
$$
:e^Q:\, \equiv \sum_{n=0}^\infty \frac{1}{n!} \oint_{\gamma_1} dz_1 \cdots \oint_{\gamma_n} dz_1 :J(z_1)\cdots J(z_n):\tag{4}
$$
The contours $\gamma_i$ are non-intersecting and radially ordered.
Define $$A_\varepsilon = \oint_\Gamma dz \,\varepsilon(z) A(z)\tag{5}$$ with $\Gamma$ larger than all $\gamma_i$.
Then do the Wick contractions
$$
\langle A_\varepsilon :e^Q: \rangle = \sum_{n=0}^\infty \frac{1}{n!} \sum_{i=1}^n \Big\langle \oint_{\gamma_1} dz_1  J(z_1) \cdots \oint_{\gamma_i} dz_i \oint_{z_i} dz\, \varepsilon(z) \overline{A(z) J(z_i)} \cdots \oint_{\gamma_n} dz_n  J(z_n)\Big\rangle\tag{6}
$$
Suppose $\langle A(z)\rangle =0$, so the sum starts at $n=1$. The singular part of the OPE in general is written as
$$
\overline{A(z) J(z_i)} = \sum_k \frac{(AJ)_k(z_i)}{(z-z_i)^k}\tag{7}
$$
Plugging this into the above formula, we see that the $z$-integral only has a pole in $z = z_i$. Does that imply we can deform the $z$-contour back to $\Gamma$? If so, can we also take out the contraction $ \oint_{\Gamma} dz\,\varepsilon(z)\oint_{\gamma_i} dz_i  \overline{A(z) J(z_i)}$ as a common factor? My confusion lies in whether radial ordering puts $\oint_{\gamma_i} dz_i  \overline{A(z) J(z_i)} \equiv B(z)$ to the left of all other $J(z_k)$ insertions or not.
Answer: Eq. (2) holds if the contraction (3) commutes with $Q$. See e.g. this related Phys.SE post.


Can a body both topple and slide?

Question: When a body topples about a point, I'm clear about the net torque acting on the body, just wondering if the toppling can happen if there is no friction or not enough friction; can there be a situation when the point of contact of the body with the ground slides and the body still topples ?
Answer: Yes you can tip an object that is sitting on a frictionless surface. Let me show you how.
Consider first the case where the object is in a vacuum in free space. To create rotation I need to apply a torque to the object. Consider now that if I push the object anywhere other than  the center of mass. For example, visualize a bar where I am pushing sideways at one end. The object will begin to rotate about the center of mass since the side with more mass resists my push more than the one with less.
Now back to your question. If you push an object at the center of mass while it is on a frictionless surface it will only slide and will not topple. However, if you push it away from the COM then as above there is a torque and the object can topple.
Note that these are not exclusive though, the object could start sliding and then topple or could start to slant over but then just slide upon finding a new balance point. It all depends on the specifics of the problem beyond the simple thought experiment above.
Comment: "the object could start sliding and then topple or could start to slant over",can both sliding and toppling happen at the same time.
Comment: Yes. Consider the frictionless case. There is nothing stopping the translational motion of the com so it it sliding but at the same time toppling if you push it away from the position of the com. Toppling and sliding are just terms we use to describe the rotational motion vs the translational motion.
Comment: If the force is applied from the left side on a block and the block both slides and topples,will the sliding take place towards right side or towards left side.
Comment: Think about it this way: the sliding is the motion that the object aquifer from the translation of the center of mass as if it were a point particle. So if we apply a force towards the left the object will move translationally or "slide" to the left as it must by Newtons 2nd law (if the net force is to the left the object will accelerate towards the left and in the no friction or low friction case there is clearly net force to left.) The toppling may also happen here and is based on the rotational motion. It's important to notice you can for most practical purposes treat them indeoendently.

Can a body both topple and slide?


Does Mysql 5 have procedures for managing hierarchical data?

Question: I use nested set model for saving hierarchical data into database table and I'm interested in if MySQL has built-in support for adding/deleting nodes or I have to write stored procedures from scratch.
Thanks.
Answer: To my knowledge MySQL does not have an inbuilt function to do this. You may have to implement your own solution.
I have implemented nested sets with stored procedures and it worked well. I believe there has been further work on the Nested Set principle with Nested intervals to address the issues regarding the high number of updates required on the insertion or deletion of a node - but this too has its own set of problems.
Answer: as @teabot says, MySQL doesn't ship with any inbuilt functionality to do this.  However, a number of sources exist which will give you more than a half decent starting point for the queries you require, so you want have to entirely roll your own.
For examples, see Working with Graphs in MySQL , the MySQL docs and maybe even Joe Celko's book.  Depending on your exact use case, you might also find that someone has done it for you (see django-mptt implementation).


PS3 Audio Output

Question: I have a PS3 connected to a computer led monitor which has no sound output so I have an Logitech 2.1 audio system connected to that monitor. I want to connect the sound sytem to the PS3 but the cable of the sound system is probably for computer (only green audio and pink microphone cable). How can I connect it to the PS3 ? Thanks and sorry for my bad english.
Answer: Something like this I imagine: http://www.cablewholesale.com/specs/35mm-to-rca/30s1-01400.htm

Take the RCA audio output from the PS3 and convert it to the 3.5mm jack you need. The adapter will need to be female/female if I'm understanding your cabling correctly.
Comment: So the white and red RCA cables will be plugged to the back side of the connecter and the green audio cable will be connected to the front. Am I right ?
Comment: Yes. You're combining the left and right channels of the RCA into one 3.5mm (headphone) stereo jack.

PS3 Audio Output


Can't update, can't install from SC 18.04

Question: I have no idea what is going on, what to check or even where to search for help other than here. The past 5 updates have all frozen at around 75% complete, and I'm trying to install Gnome Calculator and it's stuck at 99%. All other software in the past 2 weeks has failed to install too.
Comment: Updating/installing from the terminal will show error messages that tell what's wrong.
Answer: Ran sudo apt-get update and it went flawlessly, I was then offered a partial upgrade which also went flawlessly and software is now installing. I can't believe it was that simple, I feel so silly. But thanks for helping.


Is there a limit on number of Recommendations in Personalization Builder Web-Recommendations

Question: In the Web Recommendations I am getting up to 5 products when I use the number of range to set a number of items, but In case of more than 5, I don't get the items on the Preview and the Webpage.
My Webpage and Catalog has a total of 10 products
Is there a limit on number of Recommendations in Personalization Builder Web-Recommendations?
Answer: Watch exactly how your scenario order is placed. Each scenario has a limit of 100 elements. But the scenarios do not always include all elements of your product catalog. When you would include the scenario "bought bought" and there has never been a purchase this scenariolist would be empty.
Maybe you need to pay closer attention to your scenarios you have defined and if really 10 elements are in there.
Another possibility is that you have defined that exclude the other products from being inserted in the scenarios.


MacBook Pro, iCloud Drive, Time Machine and Time Capsule 2

Question: Can I use Time Machine and Time Capsule 2 to backup not only my MacBook Pro files, apps, etc. but also the files stored on my iCloud Drive for sharing with my other MacBook Pro and others?
Answer: Yes - Time Machine saves a snapshot of the locally synced files from iCloud so you should be able to recover them even if they are gone from iCloud.
Since one Time Machine destination can be connected to many Macs, you could cross share that was as well.


Does unit sphere $S$ homeomorphic to $[0,1]$

Question: Let $(\mathbb R^2, \|\cdot\|)$ be two dimensional normed space and $S=\{x\in\mathbb R^2 : \|x\|=1\}$ the unit sphere of $(\mathbb R^2, \|\cdot\|)$. Since $S$ bounded and closed  in $\mathbb R^2$ then it is compact. Does $S$ homeomorphic to the segment $[0,1]$ with usual topolgy? And if so then how to construct such an homeomorphism?
Comment: No, they are not homeomorphic. Homeomorphic means that they are "topologically the same" -- intuitively if not formally it should be clear that the sphere and the interval are very different.
Comment: There are not even homotopy equivalent (check the fundamental groups).
Answer: No, they are not. Suppose there exists a homeomorphism $f:\Bbb S^1\longrightarrow [0,1]$, let $p\in\Bbb S^1$ such that $f(p)\neq 0$ and $f(p)\neq 1$. Then $f:\Bbb S^1\setminus \{p\}\longrightarrow [0,1]\setminus\{f(p)\}$ should be still a homeomorphism. But the source is still connected whereas the target is not connected.
Comment: They are not open or closed as subset of $\Bbb R$, however they are with respect to the induced topology.
Comment: Thanks for the comment!
Comment: You wrote $\backslash \{f(q)\}$
Comment: Thanks for answer. Could you more precise. $K=[0,1]\setminus {f(p)}$ is not connected thet it can be represented in the form $A\bigcup B$, where $A,B$ nonempty disjoint closed (or open) sets. But the sets $[0,f(p))$ and $(f(p),1]$ are not closed (or open)?
Answer: Another way of showing that $S^1$ is not homeomorphic to $[0,1]$ is by analyzing auto-homeomorphisms:

Definition. A topological space $X$ is called homogenous if for any $x,y\in X$ there exists a homeomorphism $f:X\to X$ such that $f(x)=y$.

The idea here is that in a way homogenous spaces have no special points.

Lemma. Let $X,Y$ be two homeomorphic spaces. Then $X$ is homogenous if and only if $Y$ is. In other words homogeneity is a topological invariant.

I leave the proof as an exercise.
With that you can easily see that $S^1$ is indeed homogenous: treat $S^1\subseteq\mathbb{C}$ and then for any $x,y\in S^1$ a homeomorphism that we are looking for can be for example $z\mapsto zx^{-1}y$ with complex multiplication on the right side.
Now $[0,1]$ is not homogenous. Indeed, if $f:[0,1]\to[0,1]$ is a homeomorphism then $f(0)=0$ or $f(0)=1$ as a consequence of the intermediate value theorem. So $0$ and $1$ are special points in $[0,1]$.
Note that this kind of argument can be extended to any dimension: an $n$-dimensional sphere is not homeomorphic to an $m$-dimensional cube because $n$-dimensional sphere is homogenous unlike $m$-dimensional cube (boundary points on a $m$-dimensional cube are special).
Answer: Another way to see that $S^1$ and $[0,1]$ are not homeomorphic using standard topology (i.e. not using homology/homotopy) is by using the Brouwer Fixed Point Theorem, which asserts that any continuous function $$f \colon [0,1] \to [0,1]$$ has at least one fixed point $x_0$.
But any non-zero rotation map on $S^1$ is continuous without any fixed points, for instance $$r \colon S^1 \to S^1, e^{i\theta} \mapsto e^{i \theta + \varphi},$$ with $\varphi \neq 0$.


Upgrade ruby projects from 1.8.6 to 1.8.7

Question: What steps should I follow to upgrade a Ruby project from 1.8.6 to 1.8.7?
Answer: It should be mostly seamless, since it was mostly compatible changes to the api.
Still, check out the list of incompatibilities
If you start using the new methods offered by 1.8.7 (or newer!) but would like to remain compatible with 1.8.6, checkout my backports gem.
Answer: There are just method add in ruby 1.8.7 in compare to ruby 1.8.6. So if it's works with 1.8.6 it's works in ruby 1.8.7 too.
But if you are a great test suite, launch it and see if all works.
Answer: It's a point release. You shouldn't have to do anything.
Comment: Famous last words.  http://svn.ruby-lang.org/repos/ruby/tags/v1_8_7/NEWS and search on "Compatibility issues".  The Date.parse change is pretty epic in potential confusion.
Answer: hey, read this http://casperfabricius.com/site/2010/01/24/multiple-ruby-versions-with-rvm/
it takes you through the installation and setup of Ruby Version Manager - which makes it really easy to switch between different versions of ruby in linux (and mac I think) - if you are on windows, then use this, it's called pik http://github.com/vertiginous/pik/


Is there any theoretical results about the determinants of a Non-Central Wishart matrix?

Question: As we know that a Non-Central Wishart matrix is defined as
$W:=XX^T$, where $X \in \mathbb{R}^{p \times N}$, and
$X:= M + E$, with $M \in \mathbb{R}^{p \times N}$ a deterministic and non-zero matrix, and each element of $E$ obeying the normal distribution $\mathcal{N}(0,\sigma^2)$.
While on the contrary, the Central Wishart matrix can be viewed as a special case of the Non-Central one when $M=0$ as shown above.
My question is, is there any theoretical result about the determinant of this Non-Central Wishart matrix $W$? i.e., what do we know about
$det(W)=det((M+E)(M+E)^T)$
e.g. do we know about the expectation, the moment or even the concentration inequalily about this random determinant?
And what is the relationship of the determinant between Non-Central Wishart matrices and central Wishart matrices?
Answer: For more on the determinants Noncentral Wishart Matrices see Muirhead (1982,2005) Chapter 10. In particular see Theorem 10.3.7. Muirhead also argues that the moments of the determinant can be used to obtain asymptotic distributions in builds towards this in his problems 10.2 10.3 and 10.4.
Answer: upper and lower bounds for the expectation of $\log\det W$ --- with complex matrix elements, but I presume readily generalized to real matrix elements --- have been derived in On the log-determinant of noncentral Wishart matrices (2003):
if the real eigenvalues of $\sigma^{-2}MM^{\ast}$ are ordered from large to small, $\lambda_1\geq\lambda_2\cdots\geq\lambda_p$, then
$$g_N(\lambda_1)+\sum_{k=2}^{p}\psi(N-k+1)\leq E(\log\det W)-p\log\sigma^2\leq\sum_{k=1}^p g_N(\lambda_k)$$
$${\rm with}\;\;g_N(\lambda)=\log\lambda-{\rm Ei}\,(-\lambda)+\sum_{k=1}^{N-1}(-1/\lambda)^k\left[e^{-\lambda}(k-1)!-\frac{(N-1)!}{k(N-1-k)!}\right]$$
and $\psi$ the digamma function, Ei the exponential integral. Equality in the lower bound iff $\lambda_k=0$ for $k>1$.
Comment: Thank you for your answer! I'm still wondering if there is any further result about this log determinant random variable $\log\det W$? e.g., the distribution, or something like the confidence interval about this log determinant?


Is there an algorithm that produces a basis for $A^\perp$ given a basis for $A$?

Question: Let $A \subseteq \mathbb{R}^k$ denote a linear subspace with basis $\{b_0,\ldots,b_{n-1}\}.$ Suppose we wish to find a basis for the orthogonal complement $A^\perp$ with respect to the usual dot product. Is there an algorithm for doing this, that can realistically be done by hand? (For sufficiently small $n$ and $k$, of course, e.g. $n=2,k=4$). I do not demand that the basis we construct for $A^\perp$ be orthonormal or even orthogonal, since we can just run Gram-Schmidt at the end if we really want this.
Comment: If you were in a general inner product space other than $\mathbb{R}^k$ you wouldn't be able to make a meaningful algorithm, since $A$ and $A^{\perp}$ are separate direct summands, and so are essentially independent.
Answer: The idea is to take a basis of $A$, complete in any way you want to a basis of the whole space, and then do Gram-Schmidt to get an orthogonal basis out of it. The elements produced out of the elements of the basis of $A$ will stay in $A$ and now be orthogonal. The elements of the basis that were out of $A$ are still out of $A$ but now orthogonal to $A$. They, the latter subset, will be an orthogonal basis of $A^{\bot}$.
Answer: Consider the system of equations $\langle b_i,x\rangle=0,\;i=0,\ldots,n-1$. Obviously, every $x\in\mathbb{R}^k$ is in the orthogonal complement if and only if it solves the above system. So your question reduces to solving a homogeneous system of linear equations.


How to prove that the set given by $x^2 + y^2 = 1$ is connected?

Question: I have seen multiple proofs online that use continuity to prove that the set is connected. But how will we go about doing this without the use of mapping? Is there any way we can do this by using the definition of connectedness (not a union of non-empty disjoint open sets)?
Answer: Every path is an arc and hence lies in the circle. Therefore the circle is path-connected and hence connected.
Comment: Sorry, but what does "path-connected" mean?
Comment: That still uses continuity arguments.
Answer: Maybe you can, but I know of no such proof. You need to show that connectedness is preserved by continuous maps anyway (and that proof is quite trivial), to show it is a topological property, and for many applications (intermediate value theorem among others). There is no reason to avoid using it.
Comment: we're basically following the book in terms of lectures and notes. But questions are usually novel and made by the Professor himself (or taken from some other source). The question wasn't exactly about the unit circle. It just asked for a counter-example to the idea that intersection of connected sets is connected. I thought I'd use the unit circle as part of my answer.
Comment: We hadn't done continuity in class yet (we're following Rudin's book) and was wondering if there was a way of doing a proof without it. Thanks though!
Comment: @overloadedMathNerd In Rudin's book he doesn't ask in the exercises to show connectedness of the circle; he sneaks in a sort-of-continuity argument in an exercise on convex sets (but the circle isn't convex). So in the excercises you're not following Rudin, then?


How can I reliably track mouse enter and leave events?

Question: Various experiments I've carried out indicate that there is no foolproof way of responding to a 'mouseleave' event using jQuery. Two actions appear to not trigger any relevant event:

Moving the pointer away from an element very quickly
Moving the pointer off the element via some browser chrome (or out the the window entirely)

The second is by no means a show-stopper, but the first is a big problem. Is there a solution? Tracking document.mousemove and continually checking whether the cursor is over the target element?
Comment: Please post the problematic code, and what browser you notice these problems in.
Answer: i usually use hoverintent instead of hover to solve problems like this.


How to see Comet 46P/Wirtanen?

Question: I've got a Celestron Astromaster 114 telescope. I live in Los Angeles and would like to get a look at 46P/Wirtanen. Can anyone tell me when this comet is going to brightest and how best to locate it in the sky? It's my (perhaps incorrect) understanding that it is not especially bright. Any tips/hints/information would be much appreciated.

Source
Answer: If you have, or can borrow binoculars, that is probably a much better way to try to find the comet than your telescope. If it's set up like the one in the image in your question (that I've added) you don't have a computer read-out for RA/Dec or any way to position your mount accurately so that the polar axis points at polaris. The bright skies in LA will make doing so manually a bit of a challenge, and lack of previous experience doing so will make it even more of one.
Go to in-the-sky.org and then to Planetarium view. Go to the bottom right and type 46P into the Find box and it will find your object's name and then display it for you. Turn on the Alt/Az grid instead of the RA/Dec grid and you can see that 46P is about 60 degrees up at 8 PM your time. Lay on your back and take some time to look around with your binoculars.
It should set your location to Los Angeles automatically, but double check that.
You can see that there are some very bright stars lined up to make your viewing easier. First is Betelgeuse the bright corner star in Orion (do not say Betelgeuse three times in a row!) then Aldebaran the eye of the bull, then the comet.
At about 4th magnitude you should be able to see it as a green fuzzy star, unlike anything else. You can also zoom in using in-the-sky.org to see the local stars. The comet is going to be moving relative to the stars, so don't make zoomed-in print-outs and try to use them six hours or a day later.
Set up anything you have around the spot where you'll be laying down, to block lights from neighbors or the street, turn your own lights off. You are going to be looking East-Southeast about 2/3 of the way up to the zenith in the evening, and 46P will remain high in the sky most of the night.
Have fun!
Oh, the telescope! Once you've gotten good at finding 46P with binoculars and have some feel for the other stars nearby, then try the absolute lowest magnification you have on your telescope and just look around slowly. Loosen up your mount so you can move the tube by hand, and scan around until you see the blue fuzzy blob again.
Answer: Peak magnitude is "now", or a few days either side  of the 17th of December. The peak magnitude is about 4.0 (so this is not like Hale-Bopp), (assuming nothing unexpected happens) it can be found passing the Pleiades over the next few days. The waxing moon will affect the evenings, which you should consider when planning observations.
In-the-sky have an ephemeris for the comet:
Space.com have a finder chart and general discussion
Comment: That ephemeris data looks very precise, but is greek to me. I did manage to find a [video](https://www.youtube.com/watch?v=pNTOfiMjwbY) which has a lot of good general info but is hardly precise about locating the comet. There's a marginally more helpful [star chart](http://wirtanen.astro.umd.edu/46P/46P_finder_charts.shtml) from the university of maryland.
Comment: Well now would be a great time to learn what it all means.  Start by researching what "right ascension and declination" mean.
Comment: I seriously doubt I'll be able to calibrate my telescope mount's placement with sufficient accuracy to find this object with those ascension and declination values.

How to see Comet 46P/Wirtanen?