[pstricks] apparent postscript-induced crash

[Herbert Voss]

Am 04.01.2010 19:51, schrieb Zbigniew Nitecki:
> I don't understand what is going on here. The following code...

> \parametricplotThreeD(0.1,1){%
> \rt\space cos t mul %
> \rt\space sin t mul %
> 1 t dup mul sub 0.5 exp%
> }

> Error: /undefinedresult in --exp--
> Operand stack:
> 1.0 0.0 -4.76837e-07 0.5

there are some rounding errors. the reason, why you
want to calculate -4.76837e-07^0.5, which is not possible.

\parametricplotThreeD(0.1,1){
  \rt\space cos t mul
  \rt\space sin t mul
  1 t dup mul sub abs 0.5 exp % <-- abs
}

or

\parametricplotThreeD(0.1,0.9999){% 0.9999
  \rt\space cos t mul
  \rt\space sin t mul
  1 t dup mul sub 0.5 exp
}

or

\parametricplotThreeD(0.1,1){
  \rt\space cos t mul
  \rt\space sin t mul
  1 t dup mul sub abs sqrt % is a bit faster
}

Herbert