(a, b, c, d) # (e, f, g) = (ae be ce de) (af bf cf df) (ag bg cg dg)4 elements # 3 elements = 4 columns 3 rows
For A ## B, where A and B are vectors, IDL performs TRANSPOSE(A) ## B. In this case, C = A ## B is a matrix with Cij = Bi Aj.
(a, b, c, d) ## (e, f, g) =(ae af ag) (be bf bg) (ce cf cg) (de df dg4 elements ## 3 elements = 3 columns 4 rows
To compute the dot product, use TRANSPOSE(A) # B.
TRANSPOSE(a, b, c) # (e, f, g) = (ae +bf +cg)
We'll see more uses of # later.