' - - File: XII_Contour7a.txt
' - - Slope + Directed field study. 
' - - The RK-method runs into trouble around near-vertical slopes.

H{x,y} = -x^3 /3 + x - y^2
M{x,y} = -Diff[H,x] / Diff[H,y]

Fx{x,y} = Diff[H,x]  :  Fy{x,y} = Diff[H,y]
r =5 :  er = 0.2  :  sg = .3 : rt = Sqrt[10]	' For H{x,y} = 10 , (0,rt) is a solution.

PlotDirField[Fx,Fy,{-r,r,20}{-r,r,20}]

PlotSlopeField[M,{-r,r,20}{-r,r,20}{0,rt}{0,-rt}]

'  = = = = = = = = = = = Commented below for next files. = = = = = = = = = = = =
' Adjust screen for size, any arrows, etc. FIRST. During a session, these settings will
'    stay so a new graph may be compared with previous options (next few files).

'PlotContour[H,{-r,r,-r,r}{3,3}{-10,-10,1}{er,sg}]

' ( ***Be sure to enter "Enter Key" on last statement.from prevous work.***)





