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

```

• Prev by Date: Abs[] help please
• Next by Date: Re: Argument types