Difference between MATLAB's numel and length functions

Question

I know that length(x) returns max(size(x)) and numel(x) returns the total number of elements of x, but which is better for a 1 by n array? Does it matter, or are they interchangeable in this case?

EDIT: Just for kicks:

Looks like they're the same performance-wise until you get to 100k elements.

Answer 1

For a 1-by-N array, they are essentially the same. For a multidimensional array M, they can give different results:

• numel(M) is equivalent to prod(size(M)).
• length(M) is equivalent to max(size(M)). If M is empty (i.e. any dimension is 0), then length(M) is 0.

Answer 2

In that case they return the same and there's no difference. In term of performance, it depends on the inner working of arrays in MATLAB. E.g. if there are metainformations about how many elements are in the array (no matter the shape), then numel is as fast as possible, while max(size(x)) seems to need more work to obtain the same thing (retrieving sizes, and then finding the max among those). I am used to use numel in that case, but performance speech (hypothetical) apart, I would say they are interchangeable.