Solve third order, non-linear, ODE with indefinite BC's?

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SUMMARY

The discussion centers on solving the third order, non-linear, homogeneous, constant coefficient ordinary differential equation (ODE) given by y''' + y*y'' - y'^2 + 1 = 0, with boundary conditions y(0) = 0, y'(0) = 0, and y'(\infty) = 1. This equation is identified as the Falkner-Skan equation, which is noted to lack a general analytical solution according to Wikipedia. The user shares an attempt to solve the equation numerically using Mathematica, employing the NDSolve function with the Shooting method, which yields an approximate value for y''(0) of 1.233.

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Topher925
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I have a third order, non-linear, homogeneous, constant coefficient ODE that I need to solve but have no idea how to do it. To make matters worse, one of the boundary conditions are indefinite. Here's the equation,

y''' + y*y'' - y'^2 + 1 = 0

and the BC's
y(0) = 0
y'(0) = 0
y'(\infty) = 1

Does this equation have a general or analytical (non numerical) solution? I have access to Maple, just not at the moment, and would like to try and solve it analytically without computer first. Any suggestions on how to solve it? Can it be solved?
 
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Topher925 said:
I have a third order, non-linear, homogeneous, constant coefficient ODE that I need to solve but have no idea how to do it. To make matters worse, one of the boundary conditions are indefinite. Here's the equation,

y''' + y*y'' - y'^2 + 1 = 0

and the BC's
y(0) = 0
y'(0) = 0
y'(\infty) = 1

Does this equation have a general or analytical (non numerical) solution? I have access to Maple, just not at the moment, and would like to try and solve it analytically without computer first. Any suggestions on how to solve it? Can it be solved?

It's called the Falkner-Skan equation but maybe you know that already. Maybe a Google can help you. Wikipedia says it can't be solve analytically. Here's my attempt to solve it numerically in a limited range, say (0,10) in Mathematica:

Code:
myend = 10;
sols = Map[
   First[NDSolve[{y'''[t] + y[t] y''[t] - (y'[t])^2 + 1 == 0, 
       y[0] == y'[0] == 0, y'[myend] == 1}, y, t, 
      Method -> {"Shooting", 
        "StartingInitialConditions" -> {y[0] == 0, y'[0] == 0, 
          y''[0] == #}}]] &, {1.7, 1.75, 1.8}];
Plot[Evaluate[y[t] /. sols], {t, 0, myend}, 
 PlotStyle -> {Black, Blue, Green}, AspectRatio -> 4/3]

And that code returns y''(0)\approx 1.233
 
Last edited:
see attached... it solves falkner skan in maple..

any questions, fire away
 

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