ParametricPlot3D problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg110784] ParametricPlot3D problem*From*: "Juan Fernando Herrera J." <juanfhj at gmail.com>*Date*: Tue, 6 Jul 2010 05:02:32 -0400 (EDT)

I'm trying to plot electric field lines as tubes with a parametric plot. I build a list with n points as ptsA = BuildPointList[th] where th is the angle of the field line. ptsA[[1]] is then the list of points, and ptsA[[2]], ptsA[[3]] are lists giving two vectors perpendicular to the field line at each point. I go on to define F[pts_,i_,t_]:=pts[[1, i]] + pts[[2, i]] Cos[t] + pts[[3, i]] Sin[t] When I plot with ParametricPlot3D[ F[ptsA, i, t], {i, 1, n , 1}, {t, 0, 2 Pi}] I obtain a field line as a tube. But when I try plotting two lines ptsA, ptsB as ParametricPlot3D[ {F[ptsA, i, t], F[ptsB, i, t]}, {i, 1, n, 1}, {t, 0, 2 Pi}] I get ParametricPlot3D::ppfun: Argument {F[ptsA, i, t], F[ptsB, i, t]} is not a list with three or four elements. What's wrong here? Thanks Juan Herrera