Re: How to plot y=f(x) or given y interval?
- To: mathgroup at smc.vnet.net
- Subject: [mg119218] Re: How to plot y=f(x) or given y interval?
- From: Alexei Boulbitch <alexei.boulbitch at iee.lu>
- Date: Wed, 25 May 2011 06:58:50 -0400 (EDT)
Hi,
It is possible. The basis of the most simple approach is to plot it by a usual way and to determine (at least, approximately)
your interval along Ox, and then to plot by a usual way. Here the peculiarity arises, if the function is non-monotone.
Here is a simple example: assume the function is
f[x_] := x*Exp[-x] and the interval spans from y=0.1 to y=0.3.
Let us first look at the graph:
Plot[f[x], {x, 0, 5}]
and see that it is non-monotone. Let us then find the roots:
FindRoot[0.1 == x*Exp[-x], {x, 0.5}]
FindRoot[0.1 == x*Exp[-x], {x, 4}]
FindRoot[0.3 == x*Exp[-x], {x, 0.8}]
FindRoot[0.3 == x*Exp[-x], {x, 2}]
{x -> 0.111833}
{x -> 3.57715}
{x -> 0.489402}
{x -> 1.78134}
and now let us plot. We will need to form a piecewise function out of our function pieces:
pl1 = Plot[If[x<= 0.48, f[x], 0], {x, 0.11, 3.6}];
pl2 = Plot[If[x<= 0.48, 0, f[x]], {x, 1.1, 3.6}];
Show[{pl1, pl2}]
Have fun, Alexei
HI,
How can I plot a function y=f(x) for a given y interval?
Thank in advance
Araripe
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Alexei Boulbitch, Dr. habil.
Senior Scientist
Material Development
IEE S.A.
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