POWERMOD

The function calculates A = powermod(base,exponent,modulus)

rem and mod are built -in functions in MATLAB that help solve equations of the type A=mod(base^exponent,modulus) OR
A=rem(base^exponent,modulus)

But then range of values of A can be extended bu using the proposed powermod function.
Powermod function uses the repeated multiplication technique to obtain the value of A.