MATLAB Central Newsreader - dynamically creating for loops

dynamically creating for loops

Ramana Murthy — Wed, 09 Sep 2009 06:20:17 -0400

Hi
I have a problem in creating for loops
Suppose there is a variable n.(say 10)

for i1 = 1:10
    for i2 = i1-1:i1+1
         for i3 = i2-1:i2+1
          .....
               for i'n'( i.e i10 in present case) = i9-1:i9+1
                statements

           end
         end
     end..
end

How can I fix this for loops varyingly ?
Is it possible at all ?

with regards,
ramana

Re: dynamically creating for loops

Jan Simon — Wed, 09 Sep 2009 08:58:04 -0400

Dear Ramana murthy!

> I have a problem in creating for loops
> Suppose there is a variable n.(say 10)
>
> for i1 = 1:10
> for i2 = i1-1:i1+1
> for i3 = i2-1:i2+1
> .....
> for i'n'( i.e i10 in present case) = i9-1:i9+1
> statements
>
> end
> end
> end..
> end
>
> How can I fix this for loops varyingly ?
> Is it possible at all ?

It is possible! It looks like a perfect task for a recursive call of a subfunction.
If your statements depend on the variables of [i1 to i9], this vector must be one of the inputs of the function. Another input would be the parameter [n], which is e.g. reduced by 1 in each recursive call and if [n] equals 0, the statements are processed.

Of course, it is possible without recursion also using tricky constructions with a WHILE loop. Most likely the recursion is not the fastest method, but it can be really "nice".

Good luck, Jan

Re: dynamically creating for loops

qooroo — Wed, 09 Sep 2009 09:07:04 -0400

of course if n > 500 then you'll get

Maximum recursion limit of 500 reached. Use set(0,'RecursionLimit',N)
to change the limit. Be aware that exceeding your available stack space can
crash MATLAB and/or your computer.

I'd always avoid recursion if I could.

-qooroo

Re: dynamically creating for loops

Bruno Luong — Wed, 09 Sep 2009 09:18:05 -0400

"qooroo " <qoorooAT@gmailDOT.comREMOVECAPS> wrote in message <h87r7o$jub$1@fred.mathworks.com>...
> of course if n > 500 then you'll get
>
> Maximum recursion limit of 500 reached. Use set(0,'RecursionLimit',N)
> to change the limit. Be aware that exceeding your available stack space can
> crash MATLAB and/or your computer.

Unlikely, assuming each for-loop runs on 2 elements, how big is the number of combination before we run to recursive limit? 2^500 cases which is larger than 3e150 !

To OP, use NDGRID or any combination-generated tool in FEX to generate an array of combination your list of variables, then run a single for-loop on this array (or vectorize your code if you can.

Bruno

Re: dynamically creating for loops

Ramana Murthy — Wed, 09 Sep 2009 09:37:03 -0400

Hi
Thank you for your directions.
to be more detail, I 'm having the following code

alpha =5;
M = 10
cnt = 1;
for j1 = 1 + alpha : M - alpha
    for j2 = max(alpha,j1-1) : min(j1+1,M - alpha)
        for j3 = max(alpha,j2-1) : min(j2+1,M - alpha)
            ......for j'N' =
            data(cnt,:) = [j1 j2 j3 .....];
            cnt = cnt+1;
            ....
        end
    end
end

Can someone help me with code.

with regards,
ramana

Re: dynamically creating for loops

Ramana Murthy — Wed, 09 Sep 2009 09:40:04 -0400