matrix formation from two given matrix
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i want to form a diagonal matrix from two matrix, one contains the value of diagonal elements and other contains how many times it should occur.For example: a=[5 10 15] and b=[2 2 2] so the resultant matrix should look like r=[5 0 0 0 0 0;0 5 0 0 0 0;0 0 10 0 0 0;0 0 0 10 0 0;0 0 0 0 15 0;0 0 0 0 0 15]; But the problem is a and b can vary depending upon the situation or user input.
can i form such a matrix? I will highly appreciate any kind of suggestion.
Thanks, Mamun
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Walter Roberson
2014-4-18
1 个投票
"for" loop around repmat() in order to build the diagonal vector, and then diag() that.
Or just use a nested "for" loop.
更多回答（3 个）
Andrei Bobrov
2014-4-18
编辑：Andrei Bobrov
2014-4-18
a=[5 10 15 20];
b=[2 1 4 3];
x = cumsum(b);
v = zeros(x(end),1);
v(x-b+1) = 1;
out = diag(a(cumsum(v)));
1 个评论
Jos (10584)
2014-4-18
The old-school (fast) way of run length decoding :-)
Jos (10584)
2014-4-18
A = [5 10 15 20] ;
B = [2 1 4 3] ;
C = arrayfun(@(k) A(k)*eye(B(k)),1:numel(A),'un',0) ;
result = blkdiag(C{:})
1 个评论
Jos (10584)
2014-4-18
编辑：Jos (10584)
2014-4-18
or using REPMAT and DIAG (which is therefore also, probably, more memory efficient):
A = [5 10 15 20] ;
B = [2 1 4 3]
C = arrayfun(@(k) repmat(A(k),1,B(k)), 1:numel(A),'un',0) ;
result2 = diag([C{:}])
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