Traveling - can I connect this adapter?
Choosing power supply, how to get the voltage and current ratings?
How to prevent updating of a specific package? Because of  I'd like to prevent apt-get upgrade and Update Manager from updating the "libgtk2.0-0" package.   How can this be achieved? For any matrix $A$, $AA^T$ is symmetric, and thereby diagonalizable (Spectral Theorem). This implies that $AA^T$ has n linearly independent eigenvectors and therefore full rank.  Does this imply that for any matrix $A$, $AA^T$ is always invertible ? I know there is something wrong here because from the above chain we can conclude that a symmetric matrix is always invertible, which is definitely not true.  Could someone please point out where I am going wrong? What's the difference between  and ,  and ? If $|z_1|=1,|z_2|=1$, how can one prove $|1+z_1|+|1+z_2|+|1+z_1z_2|\ge2$ Excel: identifying if all values in a row are not equal I am trying to make a top down shooter that could potentially have hundreds of objects at once at one point. I need to check collision with projectiles, walls, and enemies. I am currently using ArrayLists which probably won't suffice later on and was wondering if someone had a good method or knows a good method for checking all of those objects at once. This is going to be a game for smartphones and is built in java. Any ideas would be great or if you could point me in some direction that would be fantastic.  Thanks in advance! Why do harmonics occur when you pluck a string? When you energise a taut string, the following resonant modes of vibration occur:    Plotting on the frequency domain, you can see their corresponding frequencies:    But what is the underlying physical principle? Why does this happen?  Is there any way of explaining it that could be understood by a smart 15 year old?  EDIT: I'm going to give my best attempt so far. Here goes:   We can start with sympathetic resonance. Sounding a particular frequency, a pure sinewave.  And noticing the string resonates sympathetically at the frequency of each harmonic. Say this is explained and understood. Now imagine that plucking a string is equivalent to a burst of white noise, which contains frequencies all the way through the spectrum. This could be approached backwards, by starting with random frequencies and noticing that resultant wave produced looks like white noise.   If the above is scientifically correct, then it restricts the domain of the question.  I would really like to be able to understand it scientifically and also be able to explain it intuitively.  PS Images from tar: Removing leading `/' from member names root@server # tar fcz bkup.tar.gz /home/foo/ tar: Removing leading `/' from member names   How can I solve this problem and keep the / on file names ? Subdivision Surface on curved mesh I'm trying to delete those ugly lines visible in the cylindrical shape of the lens. What is causing them is the added edge loops I made for the protruding detail with the switch. The problem is that if I delete those edges, it'll look even worse because of the n-gons. Any ideas? "This is a favorite question" tooltip when not favorite Cells not updating automatically I have a formula in a cell which counts the values in 2 other cells. Normally, after entering in the values in these 2 other cells, the formula cell updates automatically when Enter is pressed or when the cells are clicked out of.  However, for some reason, the value calculated by the formula does not update automatically. I am having to click on the formula bar, then I have to click enter for the formula cell to do its thing.  Why is this happening? I read a book back in middle school. Can't remember the name of the book or the author or anything. Tried googling all the stuff I remember, but nothing ever fit it. It had a biohazard symbol on the cover, and it was sort of holographic, a bunch of whites and blues, looked kind of like how people interpret dream sequences or warp jumps in sci-fi animation or film. The book involved three kids, and they got a message one day or something, and they eventually decoded it to be lottery numbers, and they were told to buy a submarine with it and some other things. Some weird fog starts appearing all over the place, and these white creatures start beating up on everybody else. When they lose pretty much everybody, they're just kind of sitting in the submarine, and they send a message back in time, I think. It's been a few years. Anybody know what the book is or have any hints on it? Thank you~ Set String via String.prototype function without return Is $0\,\mathrm{m}$ dimensionless? Is there a subtle difference between "somebody" and "someone", "anybody" and "anyone"? I am working with a time-series dataset that is based on demand-supply dynamics with several variables.  THe sample data for one time period is: &gt; data # A tibble: 19 x 6    Pred_error_A Pred_error_B  Pred_error_C  Pred_error_D  Pred_error_E  Pred_error_Target                  &lt;dbl&gt;         &lt;dbl&gt;          &lt;dbl&gt;      &lt;dbl&gt;      &lt;dbl&gt;           &lt;dbl&gt;  1            -0.45           1.72          -0.170      1.85       -0.01          -0.7    2            -0.45           1.72          -0.170      2.35       -0.01          -1.2    3            -0.45           1.92          -0.170      2.35       -0.01          -1      4            -0.0500         0.37          -0.12       1.65       -0.01          -1.5    5             0             -0.840         -0.12       0.950      -0.01          -1.7    6             0             -0.200         -0.12       1.35       -0.01          -1.5    7             0             -0.460         -0.12       1.35       -0.01          -1.8    8             0             -0.520         -0.12       1.05       -0.01          -1.5    9             0             -0.340         -0.12       1.05       -0.01          -1.4   10             0             -0.340         -0.12       1.35       -0.01          -1.7   11             0             -0.110         -0.12       1.05       -0.01          -1.2   12             0             -0.110         -0.12       0.850      -0.01          -1     13             0              0             -0.12       0.350      -0.01          -0.4   14             0              0             -0.12      -0.15       -0.01           0.100 15             0              0             -0.12      -0.350      -0.01           0.300 16             0              0             -0.02       0          -0.01          -0.1   17             0              0              0          0           0              0     18             0              0              0          0           0              0     19             0              0              0          0           0              0   I was working on a regression for each time period with data and wanted to find the relative importance of regressors in explaining the target variable ( Pred_error_A through E and dependent variable is Pred_error_Target ) using relaimpo package in R. However, I soon realized I can't use regression setting because of near to perfect collinearity and hence no relative importance values. Is there a way to go around this? Or, can I use any other method (instead of regression)? Any suggestions will be useful. The predictors are near to perfect and each one is important. I can't exclude any single one and I need the relative importance of all 5 regressors. I am also trying XGBoost as an alternative. However, I am not sure if it takes care of multicollinearity. Why could centering independent variables change the main effects with moderation? Non-https links to other StackExchange sites in User profile when using https Viruses: Adaptation to a new host through repeated host jumps A friend told me, during a 3 minute discussion, that viruses that are endemic in host $A$ and make repeated jumps to host $B$ but can't be transmitted between individuals of species $B$, may slowly adapt (through these repeated jumps) to be able to be transmitted between individuals of host $B$ and become epidemic.  I don't know much about epidemiology. I don't understand how a virus population that is endemic to host $A$ may adapt to host $B$ with repeated jumps while the viruses that jump to host $B$ are dead end because they cannot be transmitted further more. Or Are these viruses able to jump back to host $A$ to bring back their newly acquired adaptations to host $B$?  Also, I might misunderstand the meaning of "repeated host jumps transmission". I first thought it meant repeated jumps from a reservoir population in host $A$ to host $B$, but it is also possible that it describes the dynamic of a virus population that is adapted to jump from species to species and they actually gain this ability by keeping jumping and jumping. But then, how could a virus species get adapted to jump from species to species? I'm a bit confused…. Can you give me some hints about this process of cross-species transmission through repeated jumps? How to convert coordinates from vertex to world-space? How do I convert from object-space to world-space?  I suspect it is:  vert_os = obj.vertices[foo] vert_ws = vert_os.getPositionFromMatrix(obj.matrixWorld)   but does the matrix also handle translations, or do I need to handle that separately?  Can someone link to the relevant documentation?