## How to determine how a loop finishes

on 18 Nov 2013

on 18 Nov 2013

### Image Analyst (view profile)

Alright, so I have an assignment where I am to use the secant method to find the root of a function. I have the program written for the most part, and I'm able to find the root of a function no problem. However, I don't know how to have an output that can determine whether the loop finished because an answer was found, or if all the iterations were used and an answer was not located. I think I'm supposed to use an if/end or if/else kind of statement, but I'm not completely sure. I have the code listed below, any help would be greatly appreciated.

```syms x
func=('x^2 - 4');
A=0; % A= x(k-1)
B=10;% B= x(k)
abs_err=0.00001;
n=5; %number of iterations
f = inline(func);
C = B - ((B-A)/(f(B) - f(A)))*f(B); % C= x(k+1)
display(['   The function to be used is ' func])
fprintf('   The first guess, x(1) is equal to %g\n',A)
fprintf('   The second guess, x(2) is equal to %g\n',B)
fprintf('   The absolute approximate error, Ea, is equal to %g\n',abs_err)
fprintf('   The maximum number of iterations to conduct, n, is equal to %g\n',n)
disp(' ')
```
```while abs(f(C)) > abs_err
A=B;
B=C;
C= B - ((B-A)/(f(B) - f(A)))*f(B);
n=n+1;
if(n==1000)
break
end
end
```
```disp('Outputs')
display(['   The root of the function = ' num2str(C)])
```

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### Image Analyst (view profile)

on 18 Nov 2013
Edited by Image Analyst

### Image Analyst (view profile)

on 18 Nov 2013

After the loop:

```if n >= 1000
message = sprintf('No solution found after %d iterations.', n);
uiwait(warndlg(message));
else
message = sprintf(('Outputs\n   The root of the function = %f\n', C);
uiwait(warndlg(message));
end
```

### Chris (view profile)

on 18 Nov 2013

Thank you very much, that helped a lot.