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Re: [mg5324] A Bug in Parametric Plot ?
Posted:
Dec 1, 1996 11:31 PM


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



