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MathGroup Archive 2007

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Re: Nullcline and getting "2" values for y

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81509] Re: Nullcline and getting "2" values for y
  • From: ben <benjamin.friedrich at gmail.com>
  • Date: Wed, 26 Sep 2007 06:41:57 -0400 (EDT)
  • References: <fd7s8h$cgc$1@smc.vnet.net>

Dear Sean,

I would rather say you are plotting y against fun.

fun0=0.3;
NSolve[fun == fun0, y]
Select[Cases[y /. NSolve[fun == 0.4, y], _Real], (# > 0 && # < 1) &]

bye
Ben


On 24 Sep., 10:24, sean_incali <sean_inc... at yahoo.com> wrote:
> I have this equation I can plot using the following
>
> ClearAll["Global`*"]
>
> fun = (b c y - a y^ n + y^(1 + n))/(b + y^n);
> d = 0.1;
> c = 1;
> b = 10;
> a = 11;
> n = 5;
> ParametricPlot[{fun, (y)}, {y, 0, 1}, PlotRange -> All]
>
> I am plotting the function "fun" against values of y.
>
> When I do that I get a curvew that clearly shows that, for a given
> value of y, I should get two value for the function.
>
> How do I get what they are?
>
> If I just go..
>
> d = 0.1;
> c = 1;
> b = 10;
> a = 11;
> n = 2;
> y = 0.5;
>
> (b c y - a y^ n + y^(1 + n))/(b + y^n)
>
> I get
>
> 0.231707
>
> but starting at y=0 all the way to y= 0.6 or so, there are two values!
> (according to the graph)
>
> How do I get what those values are?
>
> Thanks for any input.
>
> sean




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