How can I fix the Error in Summation: (Attempted to access f(2); index out of bounds because numel (f)=1).

I'm attempting to compute a summation using Matlab (code below) corresponding to the attached system of equations. I get the following error:

Attempted to access f(2); index out of bounds because numel(f)=1.

Error in uniform_correction (line 16) f = (x^2)*f(i-2)/i/(i+2)

The following is the code:

function [] = uniform_correction()
u = input('linear attenuation coefficient:');
r = input('radius of cylinder:');
x = 2*u*r;
%N = 59;
%I = 25;
J = 0;
T = 0;
if (x<=18.5)   
   for i = 1:59
      if(i==1)
          f = -1*(4/(3*pi))*x;
      elseif(i==2)
          f = (x^2)/8;
      else
          f = (x^2)*f(i-2)/i/(i+2);
      end
   J = J + f;
   end
else
   for i = 1:25
       if (i==1)
           y = (3/(x^2))*(1/(x^2));
       else
           y = ((4*(i-1)-1)/(x^2))*y(i-1);
       end
   T = T + y;
   end
end
J_n = J + 1;
T_n = T + (1/(x^2));
J_n
T_n
if (x<=18.5)
    CF = J_n;
else
    CF = (4/(pi*x))*(1-T_n); 
end
CF
end

Answer 1

[Brendan Hamm]

You only ever assign a scalar value to f, and continuously overwrite the previous version which was there. Not sure what your intent is here, but I assume it should look more like:

if (x<=18.5)   
   for i = 1:59
      if(i==1)
          f(i) = -1*(4/(3*pi))*x; % Index f(i)
      elseif(i==2)
          f(i) = (x^2)/8; % Index f(i)
      else
          f(i) = (x^2)*f(i-2)/i/(i+2); % Index f(i)
      end
   J = J + f(i); % Index
   end
else
   for i = 1:25
       if (i==1)
           y(i) = (3/(x^2))*(1/(x^2)); % Index
       else
           y(i) = ((4*(i-1)-1)/(x^2))*y(i-1); %Index
       end
   T = T + y(i);
   end
end