MATLAB Answers


command in Matlab equivalent to "forall " in fortran

Asked by smabtahi on 24 May 2012
Hi Is there any command in matlab that can simpilfy such loop:
for i=1:10 A(i)=i^2 end
as I know in fortran it can be written anr run very fast as FORALL(i=1,10) A(i)=i**2
I hope similar thing can be found in Matlab too.


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2 Answers

Answer by Daniel Shub
on 24 May 2012
 Accepted Answer

The JIT accelerator that was introduced 10 years ago has sped up loops substantially, it is an unfortunate myth that MATLAB loops are slow. Vectorization can speed up some loops, but it can also slow things down. The ability to use parfor loops can also speed up things (and allow scaling) that is not easy with vectorized code.
For you case of wanting a user-defined function to be vectorized, the easy answer is to go back to the function (jmat_TM) and modify it to handle vector inputs.


Thanks Daniel and Jan
Then it seems that I have no other choise than vectorizing jmat_TM.
Or you could just stick with your loop. There is no guarantee that vectorizing will speed things up, although it will make your code for jmat_TM much more MATLAB like.

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Answer by Wayne King
on 24 May 2012

A = 1:10;
A = A.^2;


Thank you Wayne.
of course the power function in pre-defined in matlab for whole matrixes, but consider a user defined function, for instance this loops:
for id=1:10
for jmd=1:100;
and jmat_TM is a user-defined complicated function. I want to get rid of using those loops.
on 24 May 2012
You can omit the square brackest around the output here.
You need either the loops or rewrite the user defined function, that it accepts matrices as inputs. Therefore Wayne's suggestion is fine.

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