Re: Problem with Min Max between two functions

• To: mathgroup at smc.vnet.net
• Subject: [mg111318] Re: Problem with Min Max between two functions
• From: Daniel Lichtblau <danl at wolfram.com>
• Date: Tue, 27 Jul 2010 04:18:31 -0400 (EDT)

```maria giovanna dainotti wrote:
> Dear Mathgroup,
> I have the following function
> R1=1.029
> R2=3.892
> R3=8
> e1=250
> e2=11.8
> e3=80.5
> i=pi/12
> spherenear[x_,y_]:=((R3^2-x^2-y^2)^(1/2))
> spherefar[x_,y_]:=-((R3^2-x^2-y^2)^(1/2))
> emptynear[x_,y_]:=Min[Re[spherenear[x,y]],Re[(R2^2-x^2)^(1/2)+y*Tan[i]]]
> emptyfar[x_,y_]:=Max[Re[spherefar[x,y]],Re[-(R2^2-x^2)^(1/2)]+y*Tan[i]]
> jetnear[x_,y_]:=Min[Re[spherenear[x,y]],Re[(R1^2-x^2)^(1/2)+y*Tan[i]]]
> jetfar[x_,y_]:=Max[Re[spherefar[x,y]],Re[-(R1^2-x^2)^(1/2)]+y*Tan[i]]
> f[x_,y_]:=((jetnear[x,y]-jetfar[x,y])*e1+e3*(spherenear[x,y]-emptynear[x,y]+emptyfar[x,y]-spherefar[x,y])+e2*(emptynear[x,y]-jetnear[x,y]+jetfar[x,y]-emptyfar[x,y]))*Boole[-R1=EF=82=A3x=EF=82=A3R1]+((emptynear[x,y]-emptyfar[x,y])*e2+e3*(spherenear[x,y]-emptynear[x,y]+emptyfar[x,y]-spherefar[x,y]))*(Boole[-R2<x<-R1]+Boole[R2>x>R1])+(spherenear[x,y]-spherefar[x,y])*e3*(Boole[x<-R2]+Boole[x>R2])
>
> ContourPlot[f[x,y],{x,-8,8},{y,-8,8},Contours=EF=82=AE{0,100,200,300,400,500,600,700,800,900}]
>
>>From the picture you can see there is a white contours that results a bit odd, I
> think th at it comes out from the introduction of the Min and Max.
> I would like to remove this white contour. Could you help me?
> Thanks a lot for your attention
> Cheers
> Maria
>

Would help if the code above had Mathematica InputForm for Pi, ->, and <
(or maybe it is meant to be <=, but inside a numerical Boole that
distinction hardly matters). Anyway, you have discontinuous derivatives
and possibly even discontinuous functions, I'm not sure. You can get rid
of the white curves by blurring ever so slightly. One way to do this is
as below.

eps = 10^(-4);
g[x_, y_] =
f[x, y]/2 + (f[x + eps, y] + f[x - eps, y] + f[x, y + eps] +
f[x, y - eps])/8;

ContourPlot[g[x, y], {x, -8, 8}, {y, -8, 8},
Contours -> {0, 100, 200, 300, 400, 500, 600, 700, 800, 900}]

There might also be approaches using image processing functionality.

Daniel Lichtblau
Wolfram Research

```

• Prev by Date: Re: Linking my fortran subroutines with Mathematica
• Next by Date: Re: Linking my fortran subroutines with Mathematica
• Previous by thread: Problem with Min Max between two functions