Reference: OPMUL

a⋅b = OPMUL(a, b) returns the product of a and b. a and b can be real or complex numbers, vectors, or matrices. In the case of vectors, the scalar (dot) product is returned, i.e. a real or complex number. Both vectors must have the same dimension (length). Two matrices, with formats r×m and m×c, respectively, may be multiplied, according to the rules of matrix multiplication, and the result is a r×c matrix. If a is a natural number and b a string, the product is the string added to itself b times.