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Re: How to plot y=f(x) or given y interval?

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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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Re: How to plot y=f(x) or given y interval? Alexei Boulbitch <alexei.boulbitch@iee.lu> - 2011-05-25 10:59 +0000

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