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sub

Subtract two objects using fimath object

Syntax

c = sub(F,a,b)

Description

c = sub(F,a,b) subtracts objects 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 must both be fi objects and must have the same dimensions unless one is a scalar. If either a or b is scalar, then c has the dimensions of the nonscalar object.

Examples

In this example, c is the 32-bit difference of a and b with fraction length 16.

a = fi(pi);
b = fi(exp(1));
F = fimath('SumMode','SpecifyPrecision',...
		'SumWordLength',32,'SumFractionLength',16);
c = sub(F, a, b) 

c =
 
    0.4233


          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 16

More About

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Algorithms

c = sub(F,a,b) is similar to

a.fimath = F;
b.fimath = F;
c = a - b

c =
    0.4233

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 16

        RoundingMethod: Nearest
        OverflowAction: Saturate
           ProductMode: FullPrecision
               SumMode: SpecifyPrecision
         SumWordLength: 32
     SumFractionLength: 16
         CastBeforeSum: true

but not identical. When you use sub, 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.

See Also

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