[Gmsh] "For" loop with a variable incrementation step

[Christophe Geuzaine]

Lucas Blattner Martinho wrote:
> Dear Gmsh developers,
> 
> 
> I am trying to use Gmsh's "For" loop with a variable incrementation 
> step, however I am not obtaining the expected results.
> 
> For example, I expected the following Gmsh commands
> 
> step = 1.0;
> For k In {0:100:step}
> Printf("step = %f   k = %f", step, k ) >> "test.txt";
> step = step +1;
> EndFor
> 
> 
> would produce an output file called "test.txt"  containing the following 
> data:
> 
> step = 1.000000   k = 0.000000
> step = 2.000000   k = 2.000000
> step = 3.000000   k = 5.000000
> .
> .
> .
> and so on.
> 
> 
> However, the previous commands result in the following output file:
> 
> step = 1.000000   k = 0.000000
> step = 2.000000   k = 1.000000
> step = 3.000000   k = 2.000000
> step = 4.000000   k = 3.000000
> step = 5.000000   k = 4.000000
> .
> .
> .
> and so on.
> 
> 
> It seems that incrementation of the "step" variable inside the loop does 
> not result in a variable update of "k", which keeps growing with unit steps.
> 
> I found this strange behaviour while trying to emulate  a "While" loop , 
> which doesn't appear to be promptly available in Gmsh (by setting a 
> "step" variable bigger than the "for" loop's range,  when some break 
> condition is satisfied ).
> 
> 
> Am I missing something and these are in fact the expected behaviours, or 
> would this be a bug of some sort?

Indeed, it's a limitation of our implementation: we don't reevaluate the 
arguments of the For after each iteration...


> Is there a better way to work these issues around (emulating a "While" 
> loop) ?
> 

Not that can I directly think of. I am adding this issue to our TODO list.

Thanks for the feedback,

Christophe

> 
> 
> yours faithfully,
> Lucas Blattner Martinho
> **
> 
> 
> 
> 
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> 
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine