' - - File: XI_Contour5.txt

F{x,y}= x^3 * y - x * y^3
Fx{x,y} = Diff[F,x]
Fy{x,y} = Diff[F,y]

M{x,y} = - Fx{x,y} / Fy{x,y}	' Slopes from the directed field.

r = 10 :  er = 0.1 :  sg = 0.2

Ux<t> = <t,0,0> : Uy<t> = <0,t,0>  :  Uz<t> = <0,0,t>
Plot[Ux,Uy,Uz,{t,-r,r,100}]

PlotSlopeField[M,{-r,r,20}{-r,r,20}]

PlotContour[F,{-r,r,-r,r}{3,3}{-10,10,2}{er,sg}]




