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Re: beginner's question -- syntax related?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg13369] Re: [mg13284] beginner's question -- syntax related?
  • From: BobHanlon at aol.com
  • Date: Mon, 20 Jul 1998 02:50:22 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

John,

Plot[{3-Sqrt[5-4x-x^2],3+Sqrt[5-4x-x^2]}, {x, -5, 0}];

ls[x_] := {3-Sqrt[5-4x-x^2],3+Sqrt[5-4x-x^2]};

??Plot

"Plot[f, {x, xmin, xmax}] generates a plot of f as a function of x from
xmin \ to xmax. Plot[{f1, f2, ... }, {x, xmin, xmax}] plots several
functions fi." Attributes[Plot] = {HoldAll, Protected}
 
Options[Plot] = {AspectRatio -> GoldenRatio^(-1), Axes -> Automatic, 
    AxesLabel -> None, AxesOrigin -> Automatic, AxesStyle -> Automatic, 
    Background -> Automatic, ColorOutput -> Automatic, Compiled -> True,

    DefaultColor -> Automatic, Epilog -> {}, Frame -> False, 
    FrameLabel -> None, FrameStyle -> Automatic, FrameTicks ->
Automatic, 
    GridLines -> None, ImageSize -> Automatic, MaxBend -> 10., 
    PlotDivision -> 30., PlotLabel -> None, PlotPoints -> 25, 
    PlotRange -> Automatic, PlotRegion -> Automatic, PlotStyle ->
Automatic, 
    Prolog -> {}, RotateLabel -> True, Ticks -> Automatic, 
    DefaultFont :> $DefaultFont, DisplayFunction :> $DisplayFunction, 
    FormatType :> $FormatType, TextStyle :> $TextStyle}

Note that Plot has Attribute HoldAll.  You need to Evaluate the list for
Plot to work in the second form.

Plot[Evaluate[ls[x]], {x,-5,0}];

Bob Hanlon

In a message dated 7/17/98 8:53:51 AM, john at dlugosz.com wrote:

>This works:  Plot[{3-Sqrt[5-4x-x^2],3+Sqrt[5-4x-x^2]}, {x, -5, 0}]
>
>This doesn't:
>	ls := {3-Sqrt[5-4x-x^2],3+Sqrt[5-4x-x^2]}, {x, -5, 0}
>
>	Plot[ls, {x,-5,0}]
>
>Somehow, the ls isn't getting taken as the list of two expressions.  I
>tried both = and := when creating ls, with the identical effect.
>
>Clearly, I'm missing something about syntax.  Can someone help me?


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