Nimisha - unlike C/C++, indexing into MATLAB arrays begins at one instead of zero. Since your code is iterating (over m) from 0 to L, then the error message makes sense for
S(m) = a*(r^n);
I don't think that you have quite gotten this equation correct. From your attached image, it looks like
S[m] = sum(n=0...m)x[n];
which to me means that your S could be initialized as
a = 11;
r = 0.9;
L = 19;
S = zeros(L+1,1); % size S
S(1) = a*(r^0); % this corresponds to S[0] in your equation
for m = 2:L+1
S(m) = S(m-1) + a*(r^m);
end
Note how the above assumes that S is a recurrence relation. We can then plot it as
plot(S,0:L)
xlabel('Value of "S"');
ylabel('Value of "L"');
title('a = 11; r = 0.9; L = 19')
Try it and see what happens!
