MATLAB: In the program below, the loop stops at theta(4). It will be a great help if you can please help me to rectify the error.

for looploop error

clear
theta(1)= input('Enter your guess:')
theta(3)= theta(1)
S1=0.5
S2=.32
S3=0.56
dx=(1/30)
for i= 2:30
    theta(i)=(theta(i+1)+theta(i-1)+S3*(dx)^2)/(S1*theta(i)*(dx)^2+S2*(dx)^2+2)
end
theta(i)
The error message is—–
 ??? Attempted to access theta(4); index out of bounds because numel(theta)=3.
Error in ==> discrtization at 9. theta(i)=(theta(i+1)+theta(i-1)+S3*
(dx)^2)/(S1*theta(i)*(dx)^2+S2*(dx)^2+2)

Best Answer

Initialize your array theta and change the upper limit of your for loop like so:
theta = zeros(1,30);
theta(1)= input('Enter your guess:')
theta(3)= theta(1)
S1=0.5
S2=.32
S3=0.56
dx=(1/30)
for i= 2:size(theta,2)-1
      theta(i)=(theta(i+1)+theta(i-1)+S3*(dx)^2)/(S1*theta(i)*(dx)^2+S2*(dx)^2+2)
  end
theta(i)
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