Multiplying arrays to add a dimenstion

Hello,

I have a big array which represents a vector field on a surface. It's dimensions are 3xNxN. I would like to project that surface forward along these vectors, along a distance of M. So I'd like to multiply the arrays M by 3xNxN to wind up with a new array that's Mx3xNxN. I've tried a bunch of different kinds of multiplication. Do I have to give each array an extra dimension of 1? I think I could do it then, but I don't know of an easy way to add a dimension of length 1.

I know how to do this with a loop. I was hoping that there is some faster/easier way to do it with matrix operations.

[James Tursa]

What does "project along a distance of M" mean? Do you have an M-element vector that you are multiplying by? Or ...?

[Drew Elliott]

Essentially yes. I want to multiply an M vector by a 3xNxN array and get an Mx3xNxN array. The actual physics that it represents aren't really important to the Matlab Question, but if you're interested:

The vector field is made up of unit vectors, so what I'm really doing is adding M_i .* 3xNxN (vector) to 3xNxN (original position) to get p_i 3xNxN. Each p_i 3xNxN is a projection of the original surface along the vector field through the distance M_i.

Answer 1

[Walter Roberson]

permute(TheArray, [4 1 2 3]) .* TheVector(:)

The result will be numel(TheVector) by size(TheArray,1) by size(TheArray,2) by size(TheArray,3)