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MathGroup Archive 1998

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Re: Why doesn't this work ?



Hi Andreas

Plot has the attribute HoldAll. So:
> Look at this:
> 
> This works:
>   Clear[S1];
>   S1=Sin[x];
>   Plot[S1, {x, 0, 3}]
> 

Matheamtica see one single symbol S1 and assumes it has to plot one
function. S1 gets evaluated and evaluates to Sin[x] -- all works fine.

> But why doesn't it work with more than one functions ?
> 
>   Clear[S2];
>   S2={Sin[x],Cos[x]};
>   Plot[S2, {x, 0, Pi}]

Again Mathematica see one single symbol and assumes S2 will return one
value. Now S2 gets evaluated and evaluates to a pair of functions --
but now it is to late to fall back from the assumption of one single
argument and You get an error message.

To Help You out -- Just put a Evaluate[S1] to Your first
Plot[]-argument. Than  S2 is evaluated first 

Plot[Evaluate[S2],{x,0,Pi}] 

to

Plot[{Sin[x],Cos[x]},{x,0,Pi}]

and Mathematica can reconize that more than one function is to be
plotted. Hope that helps
  Jens




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