Re: errors with contour plots

*To*: mathgroup at christensen.cybernetics.net*Subject*: [mg1004] Re: errors with contour plots*From*: ianc (Ian Collier)*Date*: Mon, 8 May 1995 05:08:28 -0400*Organization*: Wolfram Research, Inc

In article <3o6trh$psn at news0.cybernetics.net>, blfishman at ucdavis.edu (Beth Fishman (Schuyler)) wrote: > please respond to me directly I use the web to read the list > > Again, I am trying to teach myself mathmatica and cannot figure out why I > am getting a certain error message. The notebook is attached. > > Any help learning mathmatica would be appreciated. I have several books, > but when I finally try to do my own problems, I get lots of erros which I > cannot decode > > thanks > > __________ > phi[x_,y_] := c f ( - y ( Cos[Pi[] p / 1000] + 1 ) + k^-1 Sin[k ( x - c t )]) > c = 1 > f = 10^-4 > p = 250 > k = 1 > t = 0 > 1 > 1 > ----- > 10000 > 250 > 1 > 0 > ContourPlot[phi[x,y], {x,0,Pi}, {y,0,Pi}] > ContourPlot::plnr: > phi[x, y] is not a machine-size real number at {x, y} > = {0., 0.}. > > -ContourGraphics- > ------------------------- > > ------------------------------------------------------------------- > Beth Fishman (Schuyler) Dept of Atmospheric Science > Graduate Student Land Air and Water Resources > blfishman at ucdavis.edu Hoagland Hall > 916-752-1868 U.C. Davis > http://atm21.ucdavis.edu/~fishman Davis CA 95616 > > "Practice senseless beauty and random acts of kindness" > ------------------------------------------------------------------- Hello, I think that the problem lies in your definition of phi[x_,y_]. The error message is telling you that it does not evaluate to a real number at {x,y} = {0.,0.} and a whole lot of other points. Your definition is: phi[x_,y_] := c f ( - y ( Cos[Pi[] p / 1000] + 1 ) + k^-1 Sin[k ( x - c t )]) ^^^^ The function Pi[] is not defined anywhere. So when ContourPlot tries to evaluate phi[0.,0.] it gets the following: In[17]:= phi[0.,0.] Out[17]= Pi[] 0. + 0. (1 + Cos[----]) 4 ----------------------- 10000 and so on for other values of x and y. There is no way of plotting this. I suspect that this is a typo. When I changed Pi[] to Pi the Mathematica name for the constant pi, it plotted without error. phi[x_,y_] := c f ( - y ( Cos[Pi p / 1000] + 1 ) + k^-1 Sin[k ( x - c t )]) I hope this helps. --Ian ---------------------------------------------------------------- Ian Collier Technical Sales Support Wolfram Research, Inc. ---------------------------------------------------------------- Tel (217) 398-0700 Fax (217) 398-0747 ianc at wri.com Wolfram Research Home Page http://www.wri.com/ ----------------------------------------------------------------