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Checking that a local expression is zero #585

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vsht opened this issue Nov 20, 2024 · 5 comments · May be fixed by #588
Open

Checking that a local expression is zero #585

vsht opened this issue Nov 20, 2024 · 5 comments · May be fixed by #588
Milestone
v4.3.2

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@vsht
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vsht commented Nov 20, 2024

Dear all,

I know that it's a stupid question, but I really wasn't able to find an elegant way solve it without complicating
everything too much. So is there a simple way to check if the given local expression is zero during the execution?

Consider for example

S a,b; 
L exp1 = a+b;
L exp2 = a*b;
.sort
id a=-b;
.sort
* More code
print;
.end

here exp1 becomes zero after the id statement, while exp2 is not zero. Ideally, I would like to detect exp1 vanishing and finish the program right here (or maybe jump to the end), instead of going through all the subsequent code instructions.

Cheers,
Vlad
@jodavies
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Yes, I think it is undocumented but you can do, e.g.,

S a,b;
L exp1 = a+b;
L exp2 = a*b;
.sort
id a=-b;
.sort
#do e = {`activeexprnames_'}
   #if `ZERO_`e''
      #message `e' is zero
   #endif
#enddo
.end

@vsht
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vsht commented Nov 20, 2024

Many thanks!

@jodavies jodavies reopened this Nov 20, 2024
@jodavies jodavies added this to the v4.3.2 milestone Nov 20, 2024
@jodavies
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We should an explanation of this (and UNCHANGED_) to the manual.

@StHagel
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StHagel commented Nov 22, 2024

Yes, I think it is undocumented but you can do, e.g.,

S a,b;
L exp1 = a+b;
L exp2 = a*b;
.sort
id a=-b;
.sort
#do e = {`activeexprnames_'}
   #if `ZERO_`e''
      #message `e' is zero
   #endif
#enddo
.end

This loops over all local expressions though, right? Is there a way to check just one specific expression?

@jodavies
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Sure, you use ZERO_exprname for whichever exprname you want.

@jodavies jodavies linked a pull request Nov 25, 2024 that will close this issue
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Add documentation for UNCHANGED_ and ZERO_ jodavies/form
3 participants
@vsht @jodavies @StHagel