is it allowed to update the cycle variable?

% for example:
for i = 1:N
i = i +3; 
end

Answer 1

[Walter Roberson]

You can change the index variable within a "for" loop, and the change in value will last to the end of the iteration. As soon as the next iteration starts the new value assigned will ignore any change you made. For example,

for K = 1 : 5
  disp(K);    %first time through would be 1, second time through would be 2
  K = K * 10;   %allowed
  disp(K);    %first time through would be 10, second time through would be 20
end

Notice that the second time through the loop the change of K from 1 to 10 in the first iteration has no effect on what happens for the second iteration.

[per isakson]

Yes, but ...

[Walter Roberson]

The question was "is it allowed" and the answer is "Yes". And now I have clarified the effect it has.

[per isakson]

Yes, your answer is correct. I don't question that.

However, the documentation says: "Avoid assigning a value to the index variable within the loop statements." And I cannot think of a good reason to do it.

[Walter Roberson]

I cannot think of a good reason to do it either.