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Re: Log(ln) Function + 2 Parameters + Greater

  • To: mathgroup at smc.vnet.net
  • Subject: [mg89301] Re: Log(ln) Function + 2 Parameters + Greater
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Wed, 4 Jun 2008 05:38:11 -0400 (EDT)

On 6/3/08 at 3:59 AM, vexie.infamous at googlemail.com (Felipe
Mannshardt) wrote:

>i am having problem telling Mathematica to:

>First Try,

>Clear[x, f] f[x_] := x (a + Log[x])^2

>a > 0 Plot[f[x], {x, -5, 5}]

>Second Try,

>f[x_] := x (a + Log[x])^2

>Plot[f[x], {x, -5, 5}] /.a-> a>0

Neither of the above will work since in neither case does your
function return a numeric value. Plot can only plot functions
that return numeric values.

>What i want is to tell Mathematica to draw a Graph of f[x] when a>0

There are several possible ways to go depending on what it is
you have in mind.

You could plot a family of curves for different a values, i.e.,

Plot[Table[x (a + Log[x])^2, {a,0,1,.2}],{x,.1,3.5}]

you could plot a surface, i.e.,

Plot3D[x (a + Log[x])^2, {x,.1,3.5},{a,0,1}]

or either create a DensityPlot or ContourPlot by using these in
place of Plot3D

or you could show a region doing

Plot[{5, x*Log[x]^2}, {x, 0.1, 3.5}, Frame -> True,
    PlotRange -> {-0.5, 5}, Axes -> None, Filling -> {1 -> {2}}]


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