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MathGroup Archive 2006

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Re: How to plot this

  • To: mathgroup at smc.vnet.net
  • Subject: [mg64445] Re: [mg64416] How to plot this
  • From: "David Park" <djmp at earthlink.net>
  • Date: Fri, 17 Feb 2006 04:11:59 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

y[x] has never been defined so how could Mathematica plot it?

Solve for y and then assign a plotting function to the result.

yplot[x_] = y /. Part[Solve[ x + y == 2*x*y, y], 1, 1]
x/(-1 + 2*x)

Needs["Graphics`Colors`"]

Plot[yplot[x], {x, 1, 3},
    Frame -> True,
    FrameLabel -> {x, y},
    PlotRange -> All,
    PlotLabel -> SequenceForm["y == ", yplot[x]],
    Background -> Linen,
    ImageSize -> {450, Automatic}];

For a plot over a domain that contains the singularity...

Plot[yplot[x], {x, -1, 3},
    Frame -> True,
    FrameLabel -> {x, y},
    Axes -> False,
    PlotRange -> Automatic,
    PlotLabel -> SequenceForm["y == ", yplot[x]],
    Background -> Linen,
    ImageSize -> {450, Automatic}];

If you want to get rid of the 'return line' you could use the DrawGraphics
package from my web site.

Needs["DrawGraphics`DrawingMaster`"]

Draw2D[
    {Draw[yplot[x], {x, -1, 3}] /. SplitLineOnVertical[10]},
    Frame -> True,
    FrameLabel -> {x, y},
    Axes -> {True, False},
    AxesStyle -> Gray,
    PlotRange -> Automatic,
    PlotLabel -> SequenceForm["y == ", yplot[x]],
    Background -> Linen,
    ImageSize -> {450, Automatic}];

If you want a faster answer to your question you could give a good email
address, otherwise there is usually a day's delay in the posted replies.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/




From: siegmund natter [mailto:nobody at nomail.com]
To: mathgroup at smc.vnet.net


Hello

Can anyone tell why this is wrong?

eqn1 = x + y == 2*x*y;
eqn1 /.y -> y[x];
Plot[y[x], {x, 1, 3}]

How do I do it correctly? (This is just an example; I want to do this
with a much more difficult equation)
Thanks a lot.

(I am using Mathematica 5.1)



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