Re: Question:Polar Field Plot

*To*: mathgroup at smc.vnet.net*Subject*: [mg21618] Re: Question:Polar Field Plot*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Tue, 18 Jan 2000 02:35:09 -0500 (EST)*Organization*: Universitaet Leipzig*References*: <85s1ag$aj5@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, ZEE MEANT NG wrote: > > I am trying to plot a 2D vector field. Equations which i have are in > polar form ie r and theta. > r^2= x^2+y^2 > Er=f(r,Theta) > Ep=g(r,Theta) > > I have changed them to cartesian form ie Ex, Ey . > and put Theta= arctan[y/x] > My plot covers the region {x,-1,1} and {y-1,1} > > Question 1: > The values of theta produced by mathematica are > -90<Theta<90 degree but what i required is theta which gives the > value from 0 to 360 degree. > I have used the if statement as follows but it does not work. > If[x >= 0, [Theta] = ArcTan[y/x], [Theta] = ArcTan[y/x] + \[Pi]]; > PlotVectorField[{Ex1, Ey1}, {x, - R, R}, > {y, - R, R }] ArcTan[x,y] ? Notice that x and y are exchanged to the C-function atan2(y,x) > > Question 2: > Using the built-in function to plot the vector field, it plots all > the field for the entire region. How do i set some constraints so > that it only plots at the desired region (eg. plot where x^2+y^2 < R) > ? > No. > I am having the same problem in the contour plot as well. I will be > very grateful if someone can advice me on how to solve the above > problems. The book by Tom Wickham-Jones has some functions to constrain a contour plot to a region. The Matheamtica code is on MathSource http://www.mathsource.com/Content/Enhancements/Graphics/3D/0208-976 Hope that helps Jens