Re: --->What is the problem with 'ParametricPlot'?

*To*: mathgroup at smc.vnet.net*Subject*: [mg4675] Re: --->What is the problem with 'ParametricPlot'?*From*: ags at seaman.cc.purdue.edu (Dave Seaman)*Date*: Thu, 22 Aug 1996 03:55:25 -0400*Organization*: Purdue University*Sender*: owner-wri-mathgroup at wolfram.com

In article <4ve8rf$iro at dragonfly.wolfram.com>, Seagull <whoami at hknet.com> wrote: >I input the followings: >x={Sin[t]}^3 >y={Cos[t]}^3 >ParametricPlot[{x, y}, {t, 0, Pi/2}] > >And got the following outputs: [ ... messages deleted ... ] >ParametricPlot::pptr: > x does not evaluate to a pair of real numbers at t = 0.. [ ... messages deleted ... ] >Can anyone tell me what is wrong? >Thanks in advance!! Your x and y should evaluate to one of two things for this example to work: 1. A real number, 2. A list consisting of a pair of real numbers. In case (2) you would be plotting two separate curves in parametric form on the same axis. However, your x and y each evaluate to something that matches neither (1) nor (2), namesly: 3. A list consisting of a single real number. That's because the Power function (represented here by "^") is listable and therefore x={Sin[t]}^3 sets x to {Sin[t]^3}, which is a one-element list. It should work much better if you remove the curly braces. Mathematica notices that the value of x is not a real number (case (1)) and therefore assumes it must match case (2) -- but then the length of the list turns out to be 1 instead of 2, hence the error message that x "does not evaluate to a pair of real numbers...." -- Dave Seaman dseaman at purdue.edu ++++ stop the execution of Mumia Abu-Jamal ++++ ++++ if you agree copy these lines to your sig ++++ ++++ see http://www.xs4all.nl/~tank/spg-l/sigaction.htm ++++ ==== [MESSAGE SEPARATOR] ====