How to solve Attempted to access (0) error.?

In attached figure, one equation is there which i need to implement.

where,

 x[n] = a* r^n

 a = 11; r = 0.9; L = 19; 0<=m<=L;  0<=n<=L

for this i have written a script.

 clear all
 a = 11;
 r = 0.9;
 L = 19;
 for m = 0:L
    for n = 0:L
         S(m) = a*(r^n);
    end
 end
 plot(S,m)
 xlabel('Value of "S"');
 ylabel('Value of "L"');
 title('a = 11; r = 0.9; L = 19')

When i run it, it gives following error

 Attempted to access (0); index must be a positive integer or logical.
 Error in Question_6 (line 8)
        S(m) = a*(r^n);

How to solve it..?

Answer 1

[Geoff Hayes]

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!

Answer 2

[Jan]

When you omit the clear all you can use the debugger to find out the reason of your problem.