[pstricks] tangential vector

[Martin Chicoine]

> Martin,
> I changed this to
> \psplotTangent{#1}{#2}{#3}%      default behaviour
> \psplotTangent{#1}{#2,#3}{#4}%   #2,#3 the x interval
> 
> http://voss.homedns.org/packages/pstricks-add/pstricks-add.tex
> 
> Herbert
> 

Good idea!