mpy

Multiply two objects using fimath object

Syntax

c = mpy(F,a,b)


Description

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.

Examples

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

Algorithms

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.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• Code generation does not support the syntax F.mpy(a,b). You must use the syntax mpy(F,a,b).

• When you provide complex inputs to the mpy function inside of a MATLAB^® Function block, you must declare the input as complex before running the simulation. To do so, go to the Ports and data manager and set the Complexity parameter for all known complex inputs to On.