multiplying each non zero element of a sparse matrix by a certain number

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Mnr 2015-11-25

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评论： Mnr 2015-11-28

Hello all,

I have a sparse matrix S with few non-zero elements in its row and columns. I have a vector P with the same number of elements as the total non-zero elements of S. I would like to multiply each non-zero element of S by a value in P. For example, let

S = [0 0 1 1;0 1 1 0;1 1 0 0; 1 0 0 1]
P = [0.7421 0.3751 1.9079 1.4141 1.4411 2.0796 2.4199 1.1002]

I would like to get

W = [0 0 0.7421 0.3751;0 1.9079 1.4141 0;1.4411 2.0796 0 0; 2.4199 0 0 1.1002]

Can somebody please help me with a fast way of doing this task? Thank you.

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Answer 1

Star Strider 2015-11-25

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https://ww2.mathworks.cn/matlabcentral/answers/257477-multiplying-each-non-zero-element-of-a-sparse-matrix-by-a-certain-number#answer_201140

在 MATLAB Online 中打开

This works — and NO LOOPS:

S = [0 0 1 1;0 1 1 0;1 1 0 0; 1 0 0 1] ;
P = [0.7421 0.3751 1.9079 1.4141 1.4411 2.0796 2.4199 1.1002];
Snz = find(S == 1);
Wv = S(Snz).*P';
W = zeros(1,numel(S));
W(Snz) = Wv;
W = reshape(W, size(S))'
W =
            0            0       0.7421       0.3751
            0       1.9079       1.4141            0
       1.4411       2.0796            0            0
       2.4199            0            0       1.1002

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Mnr 2015-11-25

Thank you!

Star Strider 2015-11-25

As always, my pleasure!

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Answer 2

James Tursa 2015-11-25

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https://ww2.mathworks.cn/matlabcentral/answers/257477-multiplying-each-non-zero-element-of-a-sparse-matrix-by-a-certain-number#answer_201185

编辑：James Tursa 2015-11-25

在 MATLAB Online 中打开

W = S;
G = logical(S);
W(G) = W(G) .* P(:);

Note: This preserves the sparse attribute of S. I.e., if S is sparse, then W will be sparse. If S is full, then W will be full.

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James Tursa 2015-11-27

在 MATLAB Online 中打开

Ah ... I didn't notice that you wanted the multiplication by rows, not columns. So some transposes will be required for this method. E.g.,

W = S';
G = logical(W);
W(G) = W(G) .* P(:);
W = W';

Mnr 2015-11-28

I really appreciate it!

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Answer 3

Stalin Samuel 2015-11-25

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S = [0 0 1 1;0 1 1 0;1 1 0 0; 1 0 0 1] ;
 P =  [0.7421 0.3751 1.9079 1.4141 1.4411 2.0796 2.4199 1.1002] ;
[r c] = size(S);
W = zeros(r,c);
n = 1;
for r1 = 1:r
    for c1 = 1:c
        if S(r1,c1)~=0
            W(r1,c1) =  S(r1,c1)*P(n) ;
            n = n+1;
        end
    end
end