Top "Matrix" questions

In mathematics, a matrix (plural matrices) is a rectangular array of numbers, symbols, or expressions, arranged in rows and columns.

Simple 3x3 matrix inverse code (C++)

What's the easiest way to compute a 3x3 matrix inverse? I'm just looking for a short code snippet that'll do …

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Performance of Java matrix math libraries?

We are computing something whose runtime is bound by matrix operations. (Some details below if interested.) This experience prompted the …

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Concatenating Matrices in R

How can I concatenate matrices of same columns but different number of rows? For example, I want to concatenate a ( …

r matrix concatenation
undefined reference to `std::ios_base::Init::Init()'

I write this code to read 3 files, TM is the size of square matrix, LER the No. of rows of …

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How do I make a matrix from a list of vectors in R?

Goal: from a list of vectors of equal length, create a matrix where each vector becomes a row. Example: > …

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Split a large dataframe into a list of data frames based on common value in column

I have a data frame with 10 columns, collecting actions of "users", where one of the columns contains an ID (not …

r performance matrix split dataframe
numpy get index where value is true

>>> ex=np.arange(30) >>> e=np.reshape(ex,[3,10]) >>> e array([[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [10, 11, 12, 13, 14, 15, 16, 17, 18, 19], [20, 21, 22, 23, 24, 25, 26, 27, 28, 29]]) >>&…

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Counting the number of non-NaN elements in a numpy ndarray in Python

I need to calculate the number of non-NaN elements in a numpy ndarray matrix. How would one efficiently do this …

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Function for 'does matrix contain value X?'

Is there a built in MATLAB function to find out if a matrix contains a certain value? (ala PHP's in_…

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R: Plotting a 3D surface from x, y, z

imagine I have a 3 columns matrix x, y, z where z is a function of x and y. I know …

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