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How can I get the number of elements per row form the matrix?

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Old   April 16, 2018, 09:26
Default How can I get the number of elements per row form the matrix?
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Klaus
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Hi,

how can I compute the number of elements of a particular row of the coefficient matrix?

I know how to compute the totals of the lower, upper and diagonal part e.g.

int elements_lower_triangle = matrix.lower().size() + matrix.diag().size();

int elements_upper_triangle = matrix.upper().size() + matrix.diag().size();

Klaus

Last edited by klausb; April 16, 2018 at 19:57.
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Old   April 16, 2018, 20:10
Default I have been thinking of modifying the following code which is used to print a matrix
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Code:
    for(int i = 0; i < matrix_.lower().size(); i++){
        int r = matrix_.lduAddr().upperAddr()[i];
        int c = matrix_.lduAddr().lowerAddr()[i];
        a[r*n + c] = matrix_.lower()[i];
    }

    for(int i = 0; i < matrix_.diag().size(); i++){
        a[i*n + i] = matrix_.diag()[i];
    }

    for(int i = 0; i < matrix_.upper().size(); i++){
        int r = matrix_.lduAddr().lowerAddr()[i];
        int c = matrix_.lduAddr().upperAddr()[i];
        a[r*n + c] = matrix_.upper()[i];
    }
It produces something like this (example):
Code:
   0  1  2  3
0  D  U  U  .
1  L  D  .  U
2  L  .  D  U
3  .  L  L  D
But I couldn't work out how to count the number of nonzero values (the L,D,Us) per row?
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Old   December 30, 2018, 16:27
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Quick note: I was looking into answering another thread of yours and while deducing how to do things, I remembered that gdbOF does what you're looking for: https://openfoamwiki.net/index.php/Contrib_gdbOF

If you look into the manual they provide, in the appendices are the pseudo-code blocks that tell how the matrices are reconstructed... which is what you're looking for here...
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