       Re: VectorPlot on a Circle

```Hi Patrick,

Thanks, but
VectorPlot[{x, y}, {x, -1, 1}, {y, -1, 1},
RegionFunction -> Function[{x, y}, x^2 + y^2 < 1]]
plots vectors on the unit disk,  I just want to define the vectors on the
unit circle.

What I would like is something like
VectorPlot[{x, y}, {x, -1, 1}, {y, -1, 1},
RegionFunction -> Function[{x, y}, x^2 + y^2 == 1]]
but this function only does a sparse plot of the vectors, and some
of them are not on the circle!

I'd like to know if Mathematica has the capability to restrict these vectors
to a one dimensional,
rather than a two dimensional region and do a decent plot.

Cheers,
Dave

-----Original Message-----
From: Patrick Scheibe
Sent: Thursday, December 16, 2010 5:08 AM
Cc: mathgroup at smc.vnet.net
Subject: [mg114805] Re: VectorPlot on a Circle

Hi,

VectorPlot[{x, y}, {x, -1, 1}, {y, -1, 1},
RegionFunction -> Function[{x, y}, x^2 + y^2 < 1]]

?

Cheers
Patrick

On Dec 16, 2010, at 11:49 AM, Dave Snead wrote:

> Hi,
>
> I'm trying to do a vector plot but confine the vectors to a unit circle.
>
> VectorPlot[
> If[Abs[x^2 + y^2 - 1] == 0, {x, y}, {0, 0}], {x, -1, 1}, {y, -1, 1}]
> only plots a couple of vectors, not the dense set of vectors that I want.
>
> and
> VectorPlot[
> If[Abs[x^2 + y^2 - 1] <.1, {x, y}, {0, 0}], {x, -1, 1}, {y, -1, 1}]
> plots lots of vectors but they're on an annulus rather than a circle.
>
> Is there any way to do this?
>
> Or more generally is there any way to confine the vectors to a curve.
> Or, kicking the dimension up by 1, can VectorPlot3D confine the vectors
> to a surface?
>
> Thanks,