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MathGroup Archive 1998

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Re: Drawing multiple curves with ParametricPlot3D



>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



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