Register to reply

Second order, nonlinear differential equation help

by cpyles1
Tags: nonlinear, second order
Share this thread:
cpyles1
#1
Sep6-11, 01:37 PM
P: 1
I've been trying to solve this one for a while. My professor wasn't even sure how to do it. Any suggestions?
y''+t*y+y*y'=sin(t)
Phys.Org News Partner Science news on Phys.org
Bees able to spot which flowers offer best rewards before landing
Classic Lewis Carroll character inspires new ecological model
When cooperation counts: Researchers find sperm benefit from grouping together in mice
jackmell
#2
Sep6-11, 05:03 PM
P: 1,666
Quote Quote by cpyles1 View Post
I've been trying to solve this one for a while. My professor wasn't even sure how to do it. Any suggestions?
y''+t*y+y*y'=sin(t)
Yeah. How about a power series solution? Huh? What do you mean that yy' thing? No? How about the Mathematica code below then. Looks pretty close to me.

Remove[a];

nmax = 25; 

myleftside = Sum[n*(n - 1)*Subscript[a, n]*t^(n - 2), {n, 0, nmax}] + 
    Sum[Subscript[a, n - 3]*t^(n - 2), {n, 3, nmax + 2}] + 
    Sum[Subscript[a, k]*Subscript[a, n - k]*(n - k)*t^(n - 1), {n, 0, nmax + 1}, {k, 0, n}]; 

myrightside = Sum[((-1)^n*t^(2*n + 1))/(2*n + 1)!, {n, 0, nmax}]; 

myclist = Flatten[Table[Solve[Coefficient[myleftside, t, n] == Coefficient[myrightside, t, n], 
      Subscript[a, n + 2]], {n, 0, nmax}]]; 

Subscript[a, 0] = 0; 
Subscript[a, 1] = 1; 

mysec = Table[Subscript[a, n] = Subscript[a, n] /. myclist, {n, 2, nmax}]; 

thef[t_] := Sum[Subscript[a, n]*t^n, {n, 0, nmax}];

p1 = Plot[thef[t], {t, 0, 2}, PlotStyle -> Red];

mysol = NDSolve[{Derivative[2][y][t] + t*y[t] + y[t]*Derivative[1][y][t] == Sin[t], y[0] == 0, 
    Derivative[1][y][0] == 1}, y, {t, 0, 2}];

p2 = Plot[y[t] /. mysol, {t, 0, 2}, PlotStyle -> Blue];

Show[{p1, p2}]


Register to reply

Related Discussions
1st order nonlinear differential equation Calculus & Beyond Homework 14
Nonlinear first order differential equation Calculus & Beyond Homework 3
2nd order nonlinear differential equation Differential Equations 20
First order nonlinear differential equation Calculus & Beyond Homework 0
Second order nonlinear differential equation Differential Equations 1