MATLAB: Multiply each column of n-by-m matrix by respective constants in m-by-1 vector

dot-multiplymatrixmultiplicationvector

I have an n-by-m matrix and an m-by-1 vector. I want to multiply each of the m columns in the matrix by a constant specified in my vector.

E.g. if I have a matrix A=[1,2;3,4;5,6] and a vector B=[0.5,2] I want to multiply all the elements in the first column of my matrix by 0.5 and alle the elements en the second column by 2. That is, I would like to get the result C=[0.5,4;1.5,8;2.5,12].

It can easily be done by a loop, but I would like to know if the is a faster way to do this. A built in functionality? Dot-multiply doesn't seem to do the trick 🙁

Thanks in advance!

– Jesper

Best Answer

C = bsxfun(@times,A,B);

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reshape(A.',1,[])

MATLAB: Plotting n-by-m matrix

Good question. I also faced this issue a few years ago, and I found the simplest solution was to append NaN onto the bottom of the matrices, e.g.:

X(end+1,:) = NaN;
Y(end+1,:) = NaN;
plot(X,Y,'-o')

This forces MATLAB to treat each column as its own "line", even if it contains only one data point, while the NaNs are of course not plotted (so you do not need a special case, the NaNs can be appended to matrices of any size). Here is an example with your data:

>> X = [1,1.1];
>> Y = [3,3.5];
>> X(end+1,:) = NaN;
>> Y(end+1,:) = NaN;
>> plot(X,Y,'-o')

Best Answer

Related Solutions

MATLAB: Sequential, row-wise reshape of an M–by–N matrix to form a 1–by–N vector

MATLAB: Plotting n-by-m matrix

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