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MathGroup Archive 2005

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Re: Plotting 2d graphs?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57181] Re: [mg57168] Plotting 2d graphs?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Fri, 20 May 2005 04:43:13 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Paul,

To plot the quadratic curve, let's first find the roots so we can better
center the plot. Notice that an equation is entered with "==" and not "=".

Solve[2x^2 + 16x + 32 == 0]
{{x -> -4}, {x -> -4}}

Since there is a double root at -4, let's plot from -24 to 16 using the Plot
statement. Notice that in the Plot statement we use only the expression that
is being plotted and not an equation.

Plot[2x^2 + 16x + 32, {x, -24, 16}];

For the ellipse we want to use ImplicitPlot and for that we have to load the
package. In ImplicitPlot we do use the equation.

Needs["Graphics`ImplicitPlot`"]

ImplicitPlot[(x - 5)^2/16 + (y + 4)^2/25 == 1, {x, 0, 10}];

For fancier plotting we could use some of the plotting options. To make the
same plot with a frame, labels and a colored background we could use...

Needs["Graphics`Colors`"]

ImplicitPlot[(x - 5)^2/16 + (y + 4)^2/25 == 1, {x, 0, 10},
    Axes -> False,
    Frame -> True,
    FrameLabel -> {x, y},
    PlotLabel -> (x - 5)^2/16 + (y + 4)^2/25 == 1,
    Background -> Linen,
    ImageSize -> 450];

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


From: Paul Hughes [mailto:psidoc at gmail.com]
To: mathgroup at smc.vnet.net


I'm having trouble using the basic 2d plot function.  I want to be
able to plot things such as a simple quadratic or ellipse:

Examples:  2x^2 + 16x + 32 = 0  (Quadratic)

(x-5)^2/16 + (y+4)^2/25 = 1  (Ellipse)

But have failed to do so, having tried every variation i can think of
to get it to work.





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