MATLAB: How to do symbolic mod operation

modulussymbolic

I try to do mod function with symbolic variables. Is there a way to do something like mod(a+b,b)=a which means that the reminder of (a+b) divided by b is a. But MATLAB doesn't allow both the parameters of the mod function be symbolic. Could someone help me?

Best Answer

When calling the mod function with symbolic inputs, the second input must be a matrix (which can be a vector or a scalar) of numbers or symbolic number.
"Divisor (denominator), specified as a number, symbolic number, or a vector or matrix of numbers or symbolic numbers."
The symbolic variable b isn't a number or symbolic number.
As for your statement that mod(a+b, b) is equal to a, that's not quite true.
a = 5;
b = 3;
equalsA = mod(a+b, b) == a % returns false

equivalentA = mod(a+b, b) == mod(a, b) % returns true

If you want to use symbolic numbers, you will need to wrap the commands that define equalsA and equivalentA in isAlways calls to convert them into true or false.
a = sym(5);
b = sym(3);
equalsA = isAlways(mod(a+b, b) == a) % returns false
equivalentA = isAlways(mod(a+b, b) == mod(a, b)) % returns true
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