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Closed 10 years ago.
Is there a formula that would get me the length of a matrix's diagonal in units? For example if the matrix is 3x3, the diagonal length would be 3.
The diagonal of an NxN matrix is always N.
The diagonal of a non-square matricies is min(nrows, ncols).
Matricies can have units (e.g. stiffness matrix in finite elements for mechanics has physical units of force/length), but I'm not sure how you mean it.
Related
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Closed 9 years ago.
How do we find the solution of x
say in
2*x=6
using R?
It must be very trivial but I cant find out the appropriate answer.
You can use the solve() function, which can actually handle multiple equations:
solve(2, 6)
The first argument is the left side of the equation, the second is the right side.
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Closed 10 years ago.
I need to represent vectors in 7- dimensional space.
How can I draw them and plot points on them?
I don't think there is a reasonable way to draw something 7-dimensional. Best thing to do is to draw several projections in fewer dimensions for instance 2 or 3. Even 4 dimensions is hard to comprehend for men.
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Closed 10 years ago.
I have boxscore data from the NFL and some of the data is obviously incorrect. For example for some games the number of sacks is negative, which is impossible. This column is named SackNumOff. How do I change any negative values in this column to zero?
Something like this:
dat$columnname[dat$columnname < 0] = 0
Replaces all negative numbers by 0. The idea is that you can use a subset [] both to extract a subset and assign values to a subset.
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Closed 10 years ago.
In many programming problems (e.g. some Project Euler problems) we are asked to report the answer as the remainder left after dividing the answer by 1,000,000,007.
Why not any other number?
Edit:
2 years later, here's what I know: the number is a big prime, and any answer to such a question is so large that it makes sense to report a remainder instead (as the number may be too large for a native datatype to handle).
Let me play a telepathist. 1000...7 are prime numbers and 1000000007 is the biggest one that fits in 32-bit integer. Since prime numbers are used to calculate hash (by finding the remainder of the division by prime), 1000000007 is good for calculating 32-bit hash.
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Closed 11 years ago.
How to calculate standard deviation of a single decimal value, in C#
I do it in SAS code as the following:
std(x y m ) = xSTD YSTD mSDT;
It is simply 0 see the wiki article.
Let X be the number
Calculate EV of [x] which is x
Subtract EV from each element in set which is [0]
Take the average of [0] which is 0
Take the square root of 0 which is 0