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MathGroup Archive 1998

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Re: Why doesn't this work ?




Andreas Keese wrote:

> Look at this:
>
> This works:
>   Clear[S1];
>   S1=Sin[x];
>   Plot[S1, {x, 0, 3}]
>
> But why doesn't it work with more than one functions ?
>
>   Clear[S2];
>   S2={Sin[x],Cos[x]};
>   Plot[S2, {x, 0, Pi}]
>
> gives an error - Mathematica complains that S2 is not a machine-size
> number.
>
> BTW: I don't want S2 to be pattern cause I want to use this as follows:
>
>   Clear[S,dx,S3,x];
>   S[x_]:={Sin[x/dx], Cos[x/dx], Sin[2*x/dx]};
>   S3=Evaluate[S[x] /. dx -> 2];
>   Plot[S3, {x, 0, Pi}];

 Andreas,
 S2={Sin[x],Cos[x]};
  Plot[S2, {x, 0, Pi}]
does not work because Mathematica does not evaluated S3 and so find out
that it must allow for a list of functions *before* it feeds in values.

S2={Sin[x],Cos[x]};
  Plot[Evaluate[S2], {x, 0, Pi}]

works becaues the first thing that is done is to evaluate S2 to
{Sin[x],Cos[x]} so that Mathematica gets the clue.

Your last example can be reorgnised so as to work:

Clear[S,dx,S3,x];
     S[x_]:={Sin[x/dx], Cos[x/dx], Sin[2*x/dx]};
     S3=S[x] /. dx -> 2;   (*Evaluate not needed*)
     Plot[Evaluate[S3], {x, 0, Pi}];


--
Allan Hayes
Training and Consulting
Leicester, UK
hay@haystack.demon.co.uk
http://www.haystack.demon.co.uk
voice: +44 (0)116 271 4198
fax: +44 (0)116 271 8642





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