Non working while loop

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Mikael Freyhult
Mikael Freyhult on 19 May 2022
Commented: Mikael Freyhult on 20 May 2022
When running the code below it seems the while loop is run through once and then executes the commands after the last end statement and ends the program.
I do not understand while the loop doesn’t actually loop until the while loop statement isn't true.
Thank you in advance
function P=fixpointiteration(val)
switch nargin
case 0
disp('0 Chosen input')
x0 = rand;
case 1
disp('1 Chosen input')
x0 = val;
otherwise
error('Unexpected input')
end
disp(x0)
f = @(x0) cos(x0);
i=0;
t = 0.00001;
x1=1;
while abs (x1-x0)>t
i=i+1
x1 = f(x0)
fprintf('x%d = %.8f\n',i,x1)
x0 = x1
end
disp('Number of iterations: ')
disp(i)

Answers (1)

Voss
Voss on 19 May 2022
Edited: Voss on 19 May 2022
The last line inside the while loop:
x0 = x1
sets x0 to x1. Therefore, when the while condition is checked again (which happens immediately), x1 and x0 are equal, so abs(x1-x0) is 0, which is not greater than t, so the loop stops iterating.
  1 Comment
Mikael Freyhult
Mikael Freyhult on 20 May 2022
I moved the x0 = x1 expression to above the x1 = f(x0) expression and now it works.
Thank you!

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