How can ı set initial value about for statement ???

Hi !

for i = initial value(normally 1):1:100
   for y = 1 : 1: 100

% I calculate something in this for and I understand that I m not in true way. 

% And I want to change initial value of my first for loop. Because I dont want to continue 

% from the last i. for example last i is 22, and I want to change it with 50.

% How can I change it in loop. ???

   end
end

Answer 1

[dpb]

Can't change the loop index variable that controls the loop inside it -- see the following demo--

>> for i=1:4,disp(['before mod: ' num2str(i)]),i=i+pi;disp(['after mod: ' num2str(i)]),end
before mod: 1
after mod: 4.1416
before mod: 2
after mod: 5.1416
before mod: 3
after mod: 6.1416
before mod: 4
after mod: 7.1416
>>

Note that despite futzing with i, when the loop started over the next iteration, Matlab reset it back to the proper next value in the loop and terminated the loop after the four iterations. This is owing to the fact that the loop conditions are evaluated BEFORE the loop begins and stored independently from the local variable referenced inside the loop body.

If you need to have a more flexible looping arrangement that computes some differing looping construct other than a for loop. Several options would be available, one that might be reasonably simple would be to place your for loop in a while something like

whileFlag=true;  % logical variable to control continuation
lp1=1; lp2=100;  % initial FOR indices
while whileFlag  % start the overall loop 
  for i=lp1:lp2
    % do stuff on i here
    if condition to change indices  % whatever causes the need to change 
      lp1=i+23;
      lp2=222;          % the new loop values
      break
    end
  end
  if condition to quit entirely  % the whole thing is now over
    whileFlag=false;
  end
end

Another solution is to not use the loop index as the reference variable at all but to compute that variable internal to the loop. This has the advantage of setting that index arbitrarily but then the overall continuation of the loop isn't necessarily going to either keep going long enough or quit when expected.

The simplest solution would really depend on just precisely you needs are which aren't fully developed in the question.

Answer 2

[Adam]

You can use a pre-defined array with a for loop.

e.g.

myArray = 22:100

for i = myArray ... end

You can't change the value of i within a for loop to skip from e.g. 22 upto 50 though all within the same for loop run as far as I am aware

[dpb]

Well, you can simulate such, though...which is another alternative (and something similar to which I'm guessing is what OP did given her comment on my earlier Answer) --

myArray = 22:100
for i = myArray
  mySkipVal1=37;  % some (possibly computed) points at which to skip
  mySkipVal2=43;
  if iswithin(i,mySkipVal1,mySkipVal2),break,end
  ...    
end

Utility function iswithin is

function flg=iswithin(x,lo,hi)
% returns T for values within range of input
% SYNTAX:
%  [log] = iswithin(x,lo,hi)
%      returns T for x between lo and hi values, inclusive

flg= (x>=lo) & (x<=hi);

Answer 3

[Ben11]

Maybe with something like this:

for k = 1:100

% add your code

        if k== 20 % add you condition here
            disp('condition violated!')
            k = 50

        end   
    end

[dpb]

Won't do what you expect--see my example above.

[Ben11]

Oh shoot thanks for pointing that out; the tests I made were not thorough enough I guess.

Answer 4

[Fatih]

I have resolved that topic. I have tried other ways but these are not success. dpb's way true. but late answer . :)) Thank you guyss.