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MathGroup Archive 2004

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Re: Oddities of Plot[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51160] Re: [mg51123] Oddities of Plot[]
  • From: Tomas Garza <tgarza01 at prodigy.net.mx>
  • Date: Wed, 6 Oct 2004 04:35:16 -0400 (EDT)
  • References: <200410050837.EAA08407@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Plot has attributes {HoldAll, Protected} (all arguments to a function are to
be maintained in an unevaluated form). Try

In[1]:=
Plot[Evaluate[primitive], {x, 0, 1}];

Tomas Garza
Mexico City

----- Original Message ----- 
From: "Roger Mason" <rmason at esd.mun.ca>
To: mathgroup at smc.vnet.net
Subject: [mg51160] [mg51123] Oddities of Plot[]


> Hello,
>
> Playing around in Mathematica 4 I came across this oddity:
>
> In[103]:=
> circle = Solve[r^2 == (x - h)^2 + (y - k)^2, y]
> Out[103]=
> {{y -> k - Sqrt[-h^2 + r^2 + 2 h x - x^2]}, {y ->
>         k + Sqrt[-h^2 + r^2 + 2 h x - x^2]}}
>
> In[104]:=
> primitivelow = y /. circle[[1]] /. {r -> 1 , h -> 0, k -> 0};
> primitivehigh = y /. circle[[2]] /. {r -> 1 , h -> 0, k -> 0};
> primitive = {primitivehigh, primitivelow}
> Out[106]=
> {1 - x^2, -1 - x^2}
>
> I don't see why this fails
>
> In[107]:=
> Plot[primitive, {x, 0, 1}]
> Plot::"plnr": "primitive is not a
> machine-size real number at x = 4.166666666666666`*^-8."
>
> while this works
>
> In[108]:=
> Plot[{1 - x^2, -1 - x^2}, {x, 0, 1}]
>
> Thanks,
>
> Roger Mason
>
>



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