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MathGroup Archive 1995

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Direction Fields

  • To: mathgroup at smc.vnet.net
  • Subject: [mg2079] Direction Fields
  • From: nprive at mbhs.edu (Nikki Prive )
  • Date: Fri, 29 Sep 1995 01:12:14 -0400
  • Organization: Montgomery Blair HS

 
I am using a Power Mac 6100/60 with Mathematica 2.2.2 in an attempt to 
create direction fields. My textbook says that to make one, I must first 
type ">>Graphics`PlotField`. However, I get two errors when I do this:
PlotVectorField::shdw:
Warning: Symbol PlotVectorField appears in multiple contexts
{Graphics`PlotField`,Global`}; definitions in context
Graphics`PlotField` may shadow or be shadowed by other defintions.
ScaleFunctions::shdw:
Warning:Symbol ScaleFunctions appears in multiple contexts
{Graphics`PlotField`,Global`}; definitions in context
Graphics`PlotField` may shadow or be shadowed by other defintions

then, when I try to plot a direction field, 
PlotVectorField[{1,y^2-xy},{x,0,20},{y,0,20},Axes->True,ScaleFunction
->(1&),Ticks->None,Frame->True],
mathematica simply echos this back to me without making a plot.

When I later try again, 
>>Graphics`PlotField`
I get
Syntax::sntxf:">>Graphics`PlotField" cannot be followed by "`".

How can I get Mathematica to make thses direction fields?
I tried typing imn verbatim an example from my textbook
and received the same result, so I assume it is  not 
my equation but something wrong with the computer or Mathematica's
setup.  Help!


Thanks in advance, 
Nikki Prive'
nprive at wam.umd.edu


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