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Why can templates only be implemented in the header file?
How do I generate a smooth random horizontal 2D tunnel? I'd like to create a smoother version of the navigable and quite natural-looking random tunnel found in .  It should ideally be...   infinite, so more can be generated as the player progresses; parametrised, allowing control of its thickness over time; made of smooth curves, not rectangles as in the above game; precomputable, as knowing its bounds in advance allows collision detection for e.g. positioning powerups inside the tunnel.   I'm looking for a generic method I could implement myself. Further parameters and optimizations are welcome.  Asking here was suggested . I think this fits in both places, as it's as much about the algorithm as about gamedev. If A and B are symmetric is AB=BA true? Question  if we have matrices $A$ and $B$ which are symmetric. Both of these satisfy: $$  A=A^T$$ Is $AB=BA$ true ?  Attempt to solve  Now if $A$ and $B$ are symmetric then $AB$ most be symmetric too.  $$ AB=(AB)^T=B^TA^T=BA $$  problem is how do you proof that if $A$ and $B$ are symmetric also $AB$ is symmetric ?  If somone could provide some insight on this that would ge highly appreciated.  Thanks,  Tuki See , page 2: the internal logic diagram for the MM74HC138.    The diagram shows logic inverters with bubbles at the input or at the output. Is there an actual difference between them? What are the differences between executing shell scripts using "source file.sh", "./file.sh", "sh file.sh", ". ./file.sh"? Taking back turns, and forgotten privileges A generic question across most board games: once a player has taken their turn (taken their finger off the piece they are playing), should they be allowed to change their mind?  Similarly, if a player forgets to take a privilege, such as an occupied building in Puerto Rico giving an extra worker, or plantation, if they remember a few moves later, should they be allowed to take the privilege?  Very few rules explicitly express how these events should be dealt with, so they are generally left up to the group. However, my group's rules will change depending on the personality of the players playing (not all members are available each time we play). I would like to make this consistent, and would appreciate feedback on how others deal with this scenario. How do I format a String in an email so Outlook will print the line breaks? I'm trying to send an email in Java but when I read the body of the email in Outlook, it's gotten rid of all my linebreaks. I'm putting \n at the ends of the lines but is there something special I need to do other than that? The receivers are always going to be using Outlook.   I found a page on microsoft.com that says there's a 'Remove line breaks' "feature" in Outlook so does this mean there's no solution to get around that other than un-checking that setting?  Thanks Is it possible to exclude questions I've already answered from the search criteria? Recently I asked if it were possible to find questions with just one answer and as a result we got an .  That's great, but ...     Is there a way to restrict the search to questions where that one answer isn't mine? That would help. :-)   It's certainly possible to search for , but it's not possible to exclude your own posts as far as I can tell:   -user:me searches for posts that . user:1-67 doesn't search for posts from user #1 to user #67, but searches for .  (And I'm not sure that will help anyway since I don't think it would be possible to simultaneously exclude 69-max(userID).) -Ericson searches for posts that , but since my last name is in the the metadata and not the searchable portion of posts: no joy.   And of course none of this will actually work to eliminate the questions that that I've answered already and want to ignore.  In general, If I'm involved in a Q&amp;A (or ) the notification procedures do a good job of keeping me up-to-date with developments.  But when I search, it's often to find questions I've not noticed before.  So being able to eliminate questions I have already answered would be a generally useful feature for me. There is a requirement in our project where they want to evaluate if it is possible to downgrade SQL Server from Enterprise to Standard edition and if a server can be decommissioned.  How can I identify which servers are suitable for downgrade? I'm currently typing a mathematical document which counts many sum symbols. I frequently use the align environment to render equations, although the default behaviour of this environment is to render the equations in displaystyle, which in my opinion wastes vertical space. I therefore have added \textstyle at the beginning of each line of math in this environment, but I'm looking for a more convenient solution.   So is there an environment that is similar to align with the exception it displays textstyle math by default ? Thank you. Universe from nothing? Why is it that   $$\lim_{n \rightarrow +\infty} \left( 1 + \frac{\lambda}{n}+ o \left( \frac{1}{n} \right) \right)^n = e^{\lambda}$$  I once remembered the justification for "ignoring" the $o(1/n)$ but can't recall it again. Recently my audio input, from USB headset and USB guitar cable have stopped working. Going into Windows 'Sounds' and enabling 'Listen to this device' outputs the audio as expected; the problem is not with the devices. However, as soon as I try to use them with any other program, discord, for example, no audio input is detected by discord.  I have tried everything I can think of and some suggestions from Googling around;   Updating everything - windows, drivers, all related software Rolling windows back to the last build Trying different USB ports Reinstalling drivers and software Running Windows troubleshooters Playing with device properties settings   But nothing seems to work, any suggestions? Probability of people attending same and different places $5$ tourists plan to attend Octoberfest. Each attends a location at random from the choices: Alpine, Bingeman, Concordia, Kitchener, Queens, Schwaben, Transylvania. Q What is the probability that two attend one location and three attend another same location?  I get that there are $\binom{5}{2}$ possibilities to create 2 groups. There are $\binom{7}{2}$ ways to choose 2 places so shouldn't it be $\frac{\binom{7}{2}\binom{5}{2}}{7^5}$? How do I install Ubuntu to a USB key? (without using Startup Disk Creator) If you are hurrying to reply, System → Administration → StartUp Disk Creator -- no, that's not what I'm talking about.   I want to try Ubuntu 11.04's Unity without touching my existing Ubuntu install.  To do this, I need to install the nVidia drivers first (sigh).  To do this, I need changes to persist a reboot.  To do this, I need to really install Ubuntu on a USB key.  How do you do that?    What I tried   I tried to make a USB key from , then boot from it, then choose "Install Ubuntu." The installer refused to install to the installation media itself. I tried, from my installed copy of Ubuntu:  sudo kvm /dev/sdb --cdrom .cache/testdrive/iso/ubuntu_natty-desktop-i386.iso   ...but the installer didn't detect the disk properly. Polling the keyboard (detect a keypress) in python How can I poll the keyboard from a console python app?  Specifically, I would like to do something akin to this in the midst of a lot of other I/O activities (socket selects, serial port access, etc.):     while 1:       # doing amazing pythonic embedded stuff       # ...        # periodically do a non-blocking check to see if       # we are being told to do something else       x = keyboard.read(1000, timeout = 0)        if len(x):           # ok, some key got pressed           # do something   What is the correct pythonic way to do this on Windows?  Also, portability to Linux wouldn't be bad, though it's not required. Is there a way in blender or an addon that allows me to select a bunch of faces (or verts) and evenly distributes (or relaxes) them into quads clean quads.  Without screwing up the vert ID/order.  Edit: I would like to have the shapes of my quads to turn into perfect squares while maintaining the volume of the object and the vertex order. During a sunny day the walls of my house warm up (no surprise). My question: how much of this warming up (if any) comes from visible light? I associate infrared with thermal energy. If my house was floating in space (to prevent any thermal exchange with its surroundings) and I installed a giant infrared (and UV) filter between it and the sun, would it still warm up (compared to its rest temperature in full darkness)? Would a 9V alkaline power a 12V DC motor? I am thinking about buying a 12V DC motor but want to keep everything, including the motor, battery, and power switch somewhat compact. I am not very knowledgeable about these kind of things and am curious whether or not my 12V DC motor would run at all on a 9V battery. Can not create SFTP user Debian 7 I have a linode and I access via ssh throw terminal. I need to create an sftp user which his default directory (and the only he can access) is /var/www/xxxxxx.com/public_html/directory  Now, I did it, but when I try to connect I get broken pipe or connection rejected by peer  What I did is this:  $ adduser --home /var/www/xxxxxx.com/public_html/directory/ username $ chown username:username /var/www/xxxxxx.com/public_html/directory/ $ chmod 755 /var/www/xxxxxx.com/public_html/directory/ $ nano /etc/ssh/sshd_config   In /etc/ssh/sshd_config I added the following lines  Match User username    ChrootDirectory /var/www/xxxxxx.com/public_html/directory/    AllowTCPForwarding no    X11Forwarding no    ForceCommand internal-sftp   What am I doing wrong?  EDIT: This is the actual error    EDIT2: this is the error in filezilla    EDIT 3: auth.log   Oct 15 17:47:11 (none) sshd[361]: fatal: bad ownership or modes for chroot directory "/var/www/xxxxxxxxxxxx.com/public_html/extras_html" One-hot vs dummy encoding in Scikit-learn There are two different ways to encoding categorical variables. Say, one categorical variable has n values.  converts it into n variables, while  converts it into n-1 variables. If we have k categorical variables, each of which has n values. One hot encoding ends up with kn variables, while dummy encoding ends up with kn-k variables.  I hear that for one-hot encoding, intercept can lead to collinearity problem, which makes the model not sound. Someone call it "".  My questions:   Scikit-learn's linear regression model allows users to disable intercept. So for one-hot encoding, should I always set fit_intercept=False? For dummy encoding, fit_intercept should always be set to True? I do not see any "warning" on the website. Since one-hot encoding generates more variables, does it have more degree of freedom than dummy encoding?