[Kst] Equation parser - a possible BUG.

Barth Netterfield netterfield at astro.utoronto.ca
Mon Nov 22 15:14:11 CET 2004

All references agree that -x^2 = (-1)*x^2. (or equivalently, -x^2 = 0 - x^2).
The following page notes also that some software packages get it right, and 
some get it wrong.  for example, bc and MS-excel do it wrong (!) but MSworks 
spreadsheet gets it right (!!)


I also have read that exponentiation is *right* associative so bc is correct 
in this one.  

So I'm pretty sure that the rules below for the patch are correct.

I would commit asap, to give a little more chance for us to also look for 


On November 21, 2004 11:55 pm, George Staikos wrote:
>    I just compared against bc(1) and it seems to behave different than you
> describe, and different than we currently do.  Therefore I wrote some
> testcases which we can use to try to more precisely define what we want. 
> We had operator ^ behaving like this:
> -x^y evaluates as: (-x)^y
> x^y^z evaluates as: (x^y)^z
> bc(1) has:
> -x^y evaluates as: (-x)^y      <------- same as we do
> x^y^z evaluates as: x^(y^z)     <---- different
> This patch changes us to evaluate like this:
> -x^y evaluates as: -(x^y)
> x^y^z evaluates as: x^(y^z)
> Now I'm not convinced that it's a good idea since it does the opposite of
> bc(1).  Can you test against other apps?  What do they do?
> Barth/Andrew: What do you think?  Should this patch go in?  If so, I won't
> commit yet, but I will continue to write testcases tomorrow.  Then I can
> commit tomorrow night if no other issues pop up.
> > Hope helping improving the KST quality,
>    Thanks!

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