*To*: mathgroup@smc.vnet.net*Subject*: [mg10633] Re: [mg10539] Drawing multiple curves with ParametricPlot3D*From*: David Withoff <withoff@wolfram.com>*Date*: Tue, 27 Jan 1998 03:09:58 -0500

>I want to display two curves from six InterpolatingFunctions > > {r1x[t], r1y[t], r1z[t], r2x[t], r2y[t], r2z[t]} > >and this works fine for me: > > ParametricPlot3D[Evaluate[{r1x[t],r1y[t],r1z[t]}/.%],{t,0,dt}] > >but > > ParametricPlot3D[ > {Evaluate[{r1x[t],r1y[t],r1z[t]}/.%], > Evaluate[{r2x[t],r2y[t],r2z[t]}/.%],{t,0,dt}},{t,0,dt}] > >doesn't work at all. I tried to vary this expression in many (also >stupid) ways, without any result. What's wrong with it? > >V o l k e r >vs@cascade.de Evaluate is relevant only if it is the head of an element in an expression that would otherwise hold its arguments unevaluated. In this example, Evaluate is the head of an element in a list {Evaluate[{r1x[t],r1y[t],r1z[t]}/.%], Evaluate[{r2x[t],r2y[t],r2z[t]}/.%],{t,0,dt}} and sence elements in a list are not normally held unevaluated, the Evaluate here has no effect. ParametricPlot3D does normally hold its arguments unevaluated (it has the HoldAll attribute), so Evaluate does have an effect when it is the head of an element in ParametricPlot3D. Dave Withoff Wolfram Research