How to use a while loop with irregular step?

2015 8 8
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更新时间：2015 8 8
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i would like to use a "while" loop ( while i<20) but with an irregular step. For example it goes this way : i=1,2,3, 5,7,9,12,15,18....it means it starts by a 1-step then by 2 then by a 3-step.

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Walter Roberson
Walter Roberson 2015-8-8

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while loops do not have steps. "for" loops can have steps but also can be irregular:
for i = [1,2,3, 5,7,9,12,15,18]

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bh dhouha
bh dhouha 2015-8-8
So is it impossible to do the thing with while? i can not change the counter inside the loop ? ( like if i>3 i=i+2 )
Walter Roberson
Walter Roberson 2015-8-8
If you do not change the value inside the loop then you have an infinite loop, so Yes, change it inside the loop in any way you prefer.
bh dhouha
bh dhouha 2015-8-8
Just a final point :) if i'm going to use the for loop as u mentioned , and the sequence is too long [1 ,2 ,3,.....2000] how can i write this case : if i in [1,5] take 1-step. if i in [6,10] take a 2-step ....etc?

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David Young
David Young 2015-8-8
编辑：David Young 2015-8-8

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You can do it with a for loop very simply:
for i = [1,2,3, 5,7,9, 12,15,18]
% < process using i >
end
By the way, some people take the view that it is unwise to use i or j as ordinary variables because of potential confusion with the imaginary unit, so it might be better to use ii or k or something.

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bh dhouha
bh dhouha 2015-8-8
The loop that i mentioned is just a simple example.But what i have in reality is much complex and needs a "while" loop not a for loop. I know the "for" loop can be used with irregular increment but the problem is does that work with the "while" loop or no ? Thanks for the answer :)
bh dhouha
bh dhouha 2015-8-8
By the way, if i'm going to use the for loop as u mentioned , and the sequence is too long [1 ,2 ,3,.....2000] how can i write this case : if i in [1,5] take 1-step. if i in [6,10] take a 2-step ....etc?

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