Modular Multiplicative Inverse function in matlab

Question

I have problem for calculate modular multiplicative inverse. example I have integer A = 151 and M = 541. 151 mod 541. inverse mod 151 to 541 is 43 how to calculate modular multiplicative inverse in matlab ?

Answer 1

This can be done using gcd and mod functions as follows:

A = 151;   M = 541;

[G, C, ~] = gcd(A,M);
if G==1  % The inverse of a(mod b) exists only if gcd(a,b)=1
    ModMultInv = mod(C,M)
else disp('Modular multiplicative inverse does not exist for these values')
end

Output:-

ModMultInv =
    43