How to multiply n matrices

stepsize = 0.01; 

time(1) = -10;

signalLength = 2000;
time(2) = 10;
N = signalLength+1;
x = time(1):stepsize:time(2);
Y = sech(x);
stem(x,Y), grid on 
eigenevalue = [];
z = [];
k = (time(2)-time(1))/(N-1);
for n = 1 : N
        eigenevalue = [eigenevalue time(1)+(n-1)*k];
        z =  [z i*exp(-1i*eigenevalue(n)*stepsize)];
        d = z;
end
for n = 1 : N
M(:,:,n) = [z(n)^2 Y(n)*stepsize*z(n); -conj(Y(n))*stepsize*z(n) 1];
end
while N >= 2
    s = mod(N,2);
    N = (N-s)/2;
    for n = 1 : (N-s),
        M(:,:,n) = M(:,:,2*n-1).*M(:,:,2*n)';
    end
    if s ~= 0
        M(:,:,N) = M(:,:,2*N-1);
    end
end
A(:,:,1) = M(:,:,1);

The matrix M is a function of z and n. What I need is I have to multiply the matrix M N times to eliminate the variable n, and then substitute the value of z.Can anybody help me with this please?