Solving a third order ODE in MATLAB

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Hi, MATLAB is quite about this command:
syms a h Y(x) g x B E T
D3Y = diff(Y, 3)
eqn = a.*D3Y -0.5*x^2*Y == (abs(Y))
D2Y = diff(Y, 2)
DY = diff(Y)
cond1 = Y(0) == 1;
cond2 = DY(0) == 0;
cond3 = D2Y(0) == 0
Y(x) = dsolve(eqn, cond1, cond2, cond3)
latex(Y(x))
Is there a limit here for solving it? Thanks

Accepted Answer

Karan Gill
Karan Gill on 12 Feb 2018
Do you not get this warning? If you got it, was the warning clear?
Warning: Unable to find explicit solution.
> In dsolve (line 201)
Y(x) =
[ empty sym ]
Try solving numerically using ode45 or similar.
  2 Comments
Karan Gill
Karan Gill on 13 Feb 2018
What do you mean by "other methods"?

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More Answers (3)


Sergio Manzetti
Sergio Manzetti on 15 Feb 2018
Edited: Sergio Manzetti on 15 Feb 2018
I tried this on wolfram, which is the equivalent of this:
syms a h Y(x) g x B E T
D3Y = diff(Y, 3)
eqn = a.*D3Y -0.5*x^2*Y == Y
D2Y = diff(Y, 2)
DY = diff(Y)
cond1 = Y(0) == 1;
cond2 = DY(0) == 0;
cond3 = D2Y(0) == 1;
Y(x) = dsolve(eqn, cond1, cond2, cond3)
latex(Y(x))
and I got a result,Z = 1/3*(exp(x) + 2*exp(-x/2)*cos((sqrt(3)*x)/2)) , however, the result is now non-visible because of std computation time exceeded.
  3 Comments
Torsten
Torsten on 15 Feb 2018
... and I'm surprised that the solution does not depend on "a".

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Sergio Manzetti
Sergio Manzetti on 15 Feb 2018
It doesn't matter, abs(Y) did not yield results with either methods, while the former, Y, yielded result only in wolfram.
  2 Comments
Sergio Manzetti
Sergio Manzetti on 15 Feb 2018
Yes, I am aware of that.
Torsten, are there alternative ways to solve:
D3y - x^2y = ay, where a is some constant?

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