MATLAB: Addtion with 2×1 Vector and 2×3 Matrix

Question

Hi,

In the 2017a documentation, I find that you can "Create an array, A, and add a column vector to it. The vector is treated as though it is a matrix of the same size as A, so that each element in the vector is added to a row in A."

https://www.mathworks.com/help/matlab/ref/plus.html

I am using an older release of Matlab (2015a) and this operation does not work for me. I get the following error:

Error using + Matrix dimensions must agree.

Can anyone tell me how to perform this operation on an older release, and exactly which release was this new functionality available?

Thanks

Answer 1

The new method was introduced in R2016b. See e.g. Loren: arithmetic-expanding. Use bsxfun for older Matlab versions:

A  = rand(2, 3)
b  = rand(2, 1)
R1 = bsxfun(@plus, A, b)  % Matlab <  2016b
R2 = A + b                % Matlab >= 2016b

bsxfun was introduced in 2007a. Before the array way expaned by repmat or ones:

R3 = A + b(:, ones(1, 3))
R4 = A + repmat(b, [1, 3])

The ones-method was processed efficiently by Matlab's JIT acceleration: The timings looked like Matlab does not waste time with creating the expanded array explicitely, but the addition was performed directly. But this is an assumption only: The JIT was never documented exactly.