[Kst] Equation parser - a possible BUG.

[George Staikos]

On Saturday 20 November 2004 09:18, Ron Daisy wrote:
> As far as I understand you are the one that wrote the equation parser of
> kst.
>
> While playing with KST I found that the equation parsing failed to parse
> correctly the following equation:
>
> 	exp(-(x-1)^2)
>
> The problem is that it performs the unary minus operator before the power
> of 2 as dictated
> by the precedence rules of arithmetics. This problem will show it self in
> all similar equation
> and seems to be critical.

   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!

-- 
George Staikos
KDE Developer				http://www.kde.org/
Staikos Computing Services Inc.		http://www.staikos.net/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: eparserfixes.patch
Type: text/x-diff
Size: 1643 bytes
Desc: not available
Url : http://mail.kde.org/pipermail/kst/attachments/20041121/7a7d1b35/eparserfixes.bin