[julia-users] Matrix Inverse Modulo N

[Jason Castiglione]

Hello All,
I have searched a bit looking for a matrix inverse modulo an integer, and 
could not find a function. Would there be any interest in adding a function?
I have needed it a fair amount. Here is a copy of a non-(optimal/efficient) 
function I wrote with bugs and all. 

Thanks,
Jason

function minvmod{T<:Integer}(Arr::Array{T,2},N)
    A=copy(Arr)
    n=size(A)[1]
    Ainv=eye(T,n)
    for i=1:n
        if gcd(A[i,i],N) != 1
            isz=true
        else
            isz=false
        end
        k=i+1
        while isz 
            if gcd(A[i,k],N) == 1
                isz=false
                A[:,i],A[:,k]=A[:,k],A[:,i]
                Ainv[:,i],Ainv[:,k]=Ainv[:,k],Ainv[:,i]
            else
                k+=1
            end
            if k>n
                return false
            end
                
        end
        
        tem=invmod(A[i,i],N)
        for j=1:n
            A[i,j]   =convert(T,mod(tem*A[i,j],N)) 
            Ainv[i,j]=convert(T,mod(tem*Ainv[i,j],N)) 
        end
        for j=union(1:i-1,i+1:n)
            if A[j,i] != convert(T,0)
                tem=A[j,i]
                for k=1:n
                    A[j,k]=convert(T,mod(A[j,k]-tem*A[i,k],N))
                    Ainv[j,k]=convert(T,mod(Ainv[j,k]-tem*Ainv[i,k],N))
                end
          
            end
        end
    end
    return Ainv
end