# Phase portrait plotting

I'm trying to plot a phase portrait for the equation:

(d^2/dt^2)y + b * (dy/dt)^2 = A, A > 0, b < 0


The first thing I did was changing dy/dt to p[y], so the equation is:

p'[y] + b * (p[y])^2 = A, A > 0, b < 0


However, when I make a stream plot and substitute for A and b, I see a blank plot. How can I fix this?

• Can you post the exact command that gives you a blank graph? – anderstood Dec 24 '17 at 20:45
• Manipulate[StreamPlot[{1, - b * (p[y])^2 + A}/. A->k /. b->m,{y,-3,3},{p,-3,3}],{k,0.1,5},{m,-5,-0.1}] – FrostahG Dec 24 '17 at 20:51
• Possible duplicate: mathematica.stackexchange.com/questions/14160/… – Michael E2 Dec 25 '17 at 0:05

You should change p[y] to p in your Manipulate-command

Manipulate[StreamPlot[{1, - b * (p(*[y] *))^2 + A}/. A->k /. b->m,{y,-3,3},{p,-3,3}],{k,0.1,5},{m,-5,-0.1}]