IDL # operator

I'm playing around with my old MSc code, as I have an idea where it might be useful. Here's something I forgot:
The # operator computes array elements by multiplying the columns of the first array by the rows of the second array. The second array must have the same number of columns as the first array has rows. The resulting array has the same number of columns as the first array and the same number of rows as the second array.