I am using Ubuntu. I want to make python3 be the default python version instead of python2. I tried many ways. For example :  Open your .bashrc file nano ~/.bashrc. Type alias python='python3' alias pip='pip3'  on to a new line at the top of the file then save the file with ctrl+o and close the file with ctrl+x. Then, back at your command line type source ~/.bashrc. Now your alias should be permanent.  I also tried : update-alternatives --remove python /usr/bin/python2 update-alternatives --install /usr/bin/python python /usr/bin/python3  But the problem didn't solve. How can I solve this issue ?
I am using Ubuntu 16.04 LTS . I have python3 installed. There are  two versions installed, python 3.4.3 and python 3.6 . Whenever I use python3 command, it takes python 3.4.3 by default. I want to use python 3.6 with python3. python3 --version shows version 3.4.3 I am installing ansible which supports version &gt; 3.5 . So, whenever, I type ansible in the terminal, it throws error because of python 3.4 sudo update-alternatives --config python3 update-alternatives: error: no alternatives for python3
If A is a finite set and B is an infinite set, then B\A is an infinite set Prove: If $A$ is a finite set and $B$ is an infinite set, then $B \setminus A$ is an infinite set.   I've tried proving the contrapositive, that if $B \setminus A$ is a finite set then $A$ is infinite or $B$ is finite, but I don't think this is the way to go. What is covariance in plain language and how is it linked to the terms dependence, correlation and variance-covariance structure with respect to repeated-measures designs? Determining the Orbits/Orbit Space of $O(3)$ on Real 3 by 3 Traceless Symmetric Matrices Let $O(n)$ be the set of $3 \times 3$ orthogonal matrices, and $S$ be the set of traceless real symmetric $3 \times 3$ matrices.  Now  $O(n)$ will act on $S$ by conjugation. Note that by the spectral theorem $ \forall A \in S$ in the orbit of $A$ there is a diagonal matrix $D=diag(\lambda_1, \lambda_2,\lambda_3)$ with $\lambda_1\le\lambda_2 \le\lambda_3 $.  Determine the all the orbits of the action &amp; the orbit space of the action.  What I've done:  Since all elements of $S$ are diagonlizable that the orbit of any element should be the orbit of its' diagonalized form because $\forall A \in S,   \exists P \in O(3)$ st  $PAP^t=D $ with $D$ a diagonal matrix and moreover for any other  $Q\in O(3)$ we get $QDQ^t=QPAP^tQ^t=(QP)A(QP)^t=RAR^t$.   And so would that imply the orbit space is just the set of traceless diagonal matrices as $tr(QDQ^t)=tr(DQ^tQ)=tr(Q)$ (cyclic property of trace) and $Q\in S$.  Any help is appreciated. Matrix $A^T A$ as sum of outer products How is the system call in Linux implemented? When I invoke a system call in user mode,how did the call get processed in OS?  Does it invoke some some executable binary or some standard library?  If yes,what kind of thing it needs to complete the call? How Triangle Law and Parallelogram law of addition of Vectors are different?Ain't they.  Please don't tell me the things written in book......give me the appropriate reason.And how do i distinguish between the two while adding vectors,what am i trying to say is i get really confused where to use parallelogram law and where triangle law  P.s:my basics are really weak though!May be the question might not be right How does the Wizard spellbook work? How do I determine what spells are in my spellbook when creating a character? Do I simply have a spellbook with all Pathfinder spells? Or if I'm creating a level 6 wizard, do I start knowing all level 6 spells, and then have to learn the rest as I play the game? How can I diagnose and repair missing drive space? I have a small ext3 / partition on a 2T drive which appears to have a discrepancy in its free space. How can I determine what is causing it and how it can be fixed.   After trying everything I could think of, I forced a fsck on boot which didn't have any affect.  I have other systems configured identically which don't exhibit this condition.  # df -h / Filesystem            Size  Used Avail Use% Mounted on /dev/sda1             9.7G  8.9G  318M  97% /  # du -shx --max-depth 1 / 5.2G    /  # lsof | awk 'BEGIN {t=0} /(deleted)/ {t+=$7} END {print t}' 0  # tune4fs -l /dev/sda1 | grep -E 'state|Free|Reserve|size|Inode' Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super large_file Filesystem state:         clean Inode count:              2621440 Reserved block count:     131029 Free blocks:              212317 Free inodes:              2487281 Block size:               4096 Fragment size:            4096 Reserved GDT blocks:      639 Inodes per group:         32768 Inode blocks per group:   1024 Reserved blocks uid:      0 (user root) Reserved blocks gid:      0 (group root) Inode size:               128   Edit:  fsck says the partition is 2% non-contiguous.  For comparison to du above (sparseness):  # du -hxs --apparent-size / 4.9G    / How to urlencode data for curl command? There has been a significant drop (90%) in traffic from Google to one of my well-established sites (6+ years) in the last week. Searches show that the top 3 wide keywords all dropped 4 spots. Searches for other keywords do not show ANY results in the first 10 to 25 pages of results, while previously one 1st or 2nd page at most.  Since there are , the question really is:  What steps are necessary to figure out what caused such a drop?  There have been no major changes during this period or the last month on the site and certainly not in the homepage which has dropped in rank. Over all the years of running this site and plenty of others, I have never experienced this. There are is duplicate content on my site and I have rigorously used canonical links for the last few years to ensure it is not misinterpreted as such. I'm working on a new edition of a book which uses a very unusual style of bibliography: Entries are sorted in author-year fashion, but then numbered per author or group of authors, e.g.:  Milnor, J.:    1. Construction of universal bundles: I, Ann. Math., (2)63:272-284 (1956).    2. Construction of universal bundles: II, Ann. Math., (2)63: 430-436 (1956).    3. On manifolds homeomorphic to the 7-sphere, Ann. Math., (2)64: 399-405       (1956).    4. The theory of characteristic classes, mimeographed, Princeton University,       Princeton, N.J., 1957. Milnor, J., and M. A. Kervaire:    1. Bernoulli numbers, homotopy groups, and a theorem of Rohlin, Proc. Intern.       Congr. Math., 1958. Milnor, J., and E. Spanier:    1. Two remarks on fibre homotopy type, Pacific J. Math., 10: 585-590 (1960).   Citations are formatted as Milnor [3], and so on.  Is there any bibtex style for something strange as this? Or can this type of bibliography be created with biblatex without too much coding? Infinite Series $1+\frac12-\frac23+\frac14+\frac15-\frac26+\cdots$ Was given the following infinite sum in class as a question, while we were talking about Taylor series expansions of $\ln(1+x)$ and $\arctan(x)$: $$1+\frac12-\frac23+\frac14+\frac15-\frac26+\cdots$$  The question isn't homework or anything, just a thought tease. I tried for a long while but couldn't find anything remotely close. Thanks in advance for the help. var functionName = function() {} vs function functionName() {} on proving bac-cab rule, $\vec{A} \times ( \vec{B} \times \vec{C})= \vec{B} (\vec{A} \cdot\vec{C})- \vec{C}(\vec{A}\cdot\vec{B})$ I noticed something when I was doing a proof of the BAC-CAB rule, and wanted to check if my intuition was correct.   First, when I actually multiplied out $\vec{B} (\vec{A} \cdot\vec{C})-\vec{C}(\vec{A}\cdot\vec{B}) $ I noticed that I got the same thing. That is, the two quantities are equal. This makes sense since they are dot products. But that further implies that the expression goes to zero.  Well, that means that $\vec{A} \times (\vec{B} \times \vec{C})$ would have to be zero too. And when I thought about it it occurred to me that $\vec{B} \times \vec{C}$ describes a vector perpendicular to both B and C; it's orthogonal. But $\vec{A} \times$ (any vector) will describe a vector perpendicular to (any vector) and in this case, that's $\vec{B} \times \vec{C}$. That is going to be parallel with the vector described by $\vec{B} \times \vec{C}$ itself and that further implies that the cross product of the two is equal to zero. Which is equal to the BAC-CAB quantity above.   So, what is the big honking flaw in my reasoning here? :-) Bump right-aligned text to next line iff no room How do I get my Mac to boot from an Ubuntu USB key? Can't install libglew-dev because libcheese and libclutter don't have the required versions I'm getting the following error message when attempting to install libglew-dev,  Reading package lists... Done Building dependency tree        Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation:  The following packages have unmet dependencies:  libcheese-gtk23 : Depends: libclutter-gtk-1.0-0 (&gt;= 0.91.8) but it is not going to be installed                    Depends: libcogl15 (&gt;= 1.15.8) but it is not going to be installed  libcheese7 : Depends: libclutter-gst-2.0-0 (&gt;= 0.10.0) but it is not going to be installed               Depends: gstreamer1.0-clutter but it is not going to be installed  libclutter-1.0-0 : Depends: libcogl-pango15 (&gt;= 1.15.8) but it is not going to be installed                     Depends: libcogl15 (&gt;= 1.15.8) but it is not going to be installed E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.   All those packages are however apparently already installed.  I have tried all possible solutions in  post, without any luck. I have not added any PPAs. The version of ubuntu is 14.04.2.  I have looked at similar posts, and tried the following:  Running  dpkg --get-selections | grep hold   prints nothing.  sudo apt-get -oDebug::pkgProblemResolver=true install -f   Gives me nothing of interest, 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Let $been(x,y)$ denote "person x has been to place y."   Express “Every person has been to 2 or more places” using quantifiers and $been(x, y)$.  This one is completely stumping me. I'm sure that I haven't come across this kind of concept before, and can't wrap my head around how I would approach it. I suspect the quantifiers should be $∀x$, $∀y$, and that it may involve negating the statement "every person has been to one or zero places," but that's as far as I can manage to go. Any help greatly appreciated. Is is possible that a software issue could be causing spotty USB-C connections on 2017 MacBook Pro? I have a 2017 MacBook Pro. It has 2 USB-C ports on the left side and I use an Aukey hub to provide more ports (4 USB, 1 HDMI, 1 USB-C) and always to connect two monitors.   I connect one monitor through the hub with the HDMI port and another directly to the MBP with a USB-C adapter. Sometimes when I connect the hub to the Mac and the 2nd monitor to the Mac, it works as it should with no problem...but more than half the time I have to connect, disconnect, jiggle, jangle, switch ports, reconnect HDMI, etc. and hopefully they will both work. OFTEN, I can only get one monitor to fire up.  Is there any kind of software fix or reset that might solve this issue? Any other thoughts welcome. Thanks. Is posting a very long quote OK for an answer? I just found  to a question on SO. While it provides a source for the (very long) quote, I do not like the fact that the answerer just posted the quote, without adding anything. Maybe add highlights/emphasis or remove uninteresting passages. Or skip the quote altogether and write a short summary. I feel, in the current form, this should have been a comment that just links to the original article.  Am I too pedantic? Should I flag this as not an answer? Should I downvote it? What do you think about such answers?