multiplying each non zero element of a sparse matrix by a certain number
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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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Accepted Answer
Star Strider
on 25 Nov 2015
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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More Answers (2)
James Tursa
on 25 Nov 2015
Edited: James Tursa
on 25 Nov 2015
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
on 27 Nov 2015
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';
Stalin Samuel
on 25 Nov 2015
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
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