Re: How to plot this

• To: mathgroup at smc.vnet.net
• Subject: [mg64454] Re: How to plot this
• From: Jon Harrop <usenet at jdh30.plus.com>
• Date: Fri, 17 Feb 2006 04:12:35 -0500 (EST)
• References: <dt1coe\$5j\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```siegmund natter wrote:
> 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.

You can solve for y to get an expression for y[x]:

In[1]:= eqn1 = x + y == 2*x*y;

In[2]:= y[x_] = First[y /. Solve[eqn1, {y}]]

x
Out[2]= --------
-1 + 2 x

which you can then plot:

In[3]:= Plot[y[x], {x, 1, 3}];

You could also use something like InequalityPlot to highlight the same
border:

In[4]:= << Graphics`InequalityGraphics`

In[5]:= InequalityPlot[x + y < 2*x*y , {x, -3, 3}, {y, -3, 3}];

--
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/products/ocaml_for_scientists/chapter1.html

```

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