Multiply two objects using fimath object
c = mpy(F,a,b)
c = mpy(F,a,b) performs elementwise multiplication on a and b using fimath object F. This is helpful in cases when you want to override the fimath objects of a and b, or if the fimath properties associated with a and b are different. The output fi object c has no local fimath.
a and b can both be fi objects with the same dimensions unless one is a scalar. If either a or b is scalar, then c has the dimensions of the nonscalar object. a and b can also be doubles, singles, or integers.
In this example, c is the 40-bit product of a and b with fraction length 30.
a = fi(pi); b = fi(exp(1)); F = fimath('ProductMode','SpecifyPrecision',... 'ProductWordLength',40,'ProductFractionLength',30); c = mpy(F, a, b)
c = 8.5397 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 40 FractionLength: 30
c = mpy(F,a,b) is similar to
a.fimath = F; b.fimath = F; c = a .* b c = 8.5397 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 40 FractionLength: 30 RoundingMethod: nearest OverflowAction: saturate ProductMode: SpecifyPrecision ProductWordLength: 40 ProductFractionLength: 30 SumMode: FullPrecision
but not identical. When you use mpy, the fimath properties of a and b are not modified, and the output fi object c has no local fimath. When you use the syntax c = a .* b, where a and b have their own fimath objects, the output fi object c gets assigned the same fimath object as inputs a and b. See fimath Rules for Fixed-Point Arithmetic in the Fixed-Point Designer™ User's Guide for more information.