Multiplying even and odd columns separately?

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Joe Smith
Joe Smith 2015-3-6
编辑： Stephen23 2015-5-22
I have a matrix called 'displacements'
It has 50 columns
I want to multiply all the even columns by 5 and all the odd columns by 8
Anyone know a quick way to do this?

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回答（2 个）

Stephen23
Stephen23 2015-3-6
编辑：Stephen23 2015-5-22
You could do this directly using matrix indexing :
>> A = rand(4,50);
>> A(:,1:2:end) = A(:,1:2:end) * 8;
>> A(:,2:2:end) = A(:,2:2:end) * 5;
Or using bsxfun and repmat:
>> B = bsxfun(@times, A, repmat([8,5],1,25));
Giorgos Papakonstantinou
Here is one way:
A =rand(100, 50);
idx = mod(1:size(A,2), 2) ==1; % logical indexing of the odd numbers
theodd = A(:, idx)*8;
theeven = A(:, ~idx)*5;

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