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

changeexprforfor loopinitialloopsparforurgentvalue

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

Best Answer

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.
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