Re: A Bug in Parametric Plot ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg5376] Re: [mg5324] A Bug in Parametric Plot ?*From*: Andrei Constantinescu <constant at athena.polytechnique.fr>*Date*: Thu, 5 Dec 1996 14:50:18 -0500*Sender*: owner-wri-mathgroup at wolfram.com

I might say, there is no bug in ParametricPlot ! Surely, :-) , you might say there is a bug, because you get the nice figures as you say, and not the circle as we might expect. But lets look a little deeper how ParametricPlot functions: - you give {x[t], y[t]} and {t, a, b} - Mma samples the interval {t, a , b } and computes for each t_i {x[t_i], y[t_i]} - then the whole list comes in a Line object: Line[ list_of_points={....{x[t_i], y[t_i]} , .....} ] - and draws the line with Show & Graphics commands. What happens when you choose a large interval ? - the time samples are at large distances (the t_i) , and the geometric points (the {x[t_i], y[t_i]}) are also espaced ! So that a line between two of them is more a diameter than a little cord. This gives the nice plot. So for special K , and special number of sampling points you can get just a triangle ! In order to change this, try to change the PlotPoints options in ParametricPlot ! In[4]:= ParametricPlot[{Cos[t], Sin[t]} , {t, -1280 Pi, 1280 Pi}, PlotPoints -> 100 ] Out[4]= -Graphics- In[5]:= Warning: Cannot convert string "9x15B" to type FontStruct ParametricPlot[{Cos[t], Sin[t]} , {t, -1280 Pi, 1280 Pi}, PlotPoints -> 300 ] Out[5]= -Graphics- a + andrei