Re: Problem with graphics

*To*: mathgroup at smc.vnet.net*Subject*: [mg45936] Re: [mg45897] Problem with graphics*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Fri, 30 Jan 2004 04:16:06 -0500 (EST)*References*: <200401291034.FAA09688@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 29 Jan 2004, at 11:34, Lautaro Vergara wrote: > Dear people, > > I have found the following problem. I have ploted > > f[x_, y_] := Sqrt[(x^2 + y^2)^3] > > with Plot3D in order to see how it looks. Then I ploted f[x, 0] (which > is x^3) between -1 and 1 and I got a symmetric plot. It seems that > Mathematica plot the function Sqrt[x^6] or (x^2)^(3/2) and evaluate > first the symmetric term (x^6 or x^2)... > Does anyone knows what it happens and how can it be fixed? > > Thanks in advance! > > Lautaro Vergara > The problem is that f[x,0] is not, as you think, x^3 but In[2]:= f[x, 0] Out[2]= Sqrt[x^6] This means that In[6]:= f[-1,0] Out[6]= 1 and not -1. This is not Mathematica's falut but the usual convention in mathematics. I suppose what you want is: f[x_, y_] := PowerExpand[Sqrt[(x^2 + y^2)^3]] which will produce the graph you are asking for. However, I suggest you carefully check tha tis really what you need for this contradicts the usual conventions and looks rather dubious to me. Andrzej Kozlowski Chiba, Japan http://www.mimuw.edu.pl/~akoz/

**References**:**Problem with graphics***From:*Lautaro Vergara <lvergara@lauca.usach.cl>