Question

How can I find the index of the maximum element in an array without looping?

For example, if I have:

a = [1 2 999 3];

I want to define a function indexMax so that indexMax(a) would return 3.

Likewise for defining indexMin.

Answer 1

As pointed by Evgeni max and min can return the argmax and argmin as second arguments.
It is worth while noting that you can use these functions along specific dimensions:

 A = rand(4); % 4x4 matrix
 [ row_max row_argmax ] = max( A, [], 2 ); % max for each row - 2nd dimension
 [ col_min col_argmin ] = min( A, [], 1 ); % min for each column - 1st dimension

Note the empty [] second argument – it is crucial max( A, [], 2 ) is not at all equivalent to max( A, 2 ) (I’ll leave it to you as a small exercise to see what max( A, 2 ) does).

The argmax/argmin returned from these “along dimension” calls are row/col indices.