IACCUM = -1, [C] = [C] - [A][B],IACCUM = 0, [C] = [A][B],
IACCUM = +1, [C] = [C] + [A][B] .
By default (IACCUM=0), the contents of the product [A][B] are overwritten on the output matrix [C]. If IACCUM does not equal 0, the product is added or subtracted from [C], according to the sign of IACCUM.
Currently this Parameter is used by the Vectors-Vectors multiply routines RSDVVM, RNDVVM, CHDVVM, CSDVVM, CNDVVM.