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Question: How to Solve a system of coupled ODEs in Maple ?

Question:How to Solve a system of coupled ODEs in Maple ?

Mayo_Kun 5 Maple 2016
ode dsolve numeric differential-equations bvp
September 08 2019
1

Hello,

I am trying to solve a set of coupled ODEs in the following code (ODE_Prob.mw). But I am getting an error.

Please, what does this error mean and what is the solution.

Thanks in advance. 
 

> 

restart; PDEtools[declare](f(eta), prime = eta, theta(eta), prime = eta); Digits := 16; inf := 9

f(eta)*`will now be displayed as`*f

  

`derivatives with respect to`*eta*`of functions of one variable will now be displayed with '`

  

theta(eta)*`will now be displayed as`*theta

 (1)
> 

equ1 := (2*n+1)*f(eta)*(diff(theta(eta), eta))/(2*(n+1)) = (diff(theta(eta), eta, eta))/Pr^(2/(n+1))

(2*n+1)*f(eta)*(diff(theta(eta), eta))/(2*n+2) = (diff(diff(theta(eta), eta), eta))/Pr^(2/(n+1))

 (2)
> 

equ2 := (1/2)*(diff(f(eta), eta))^2-(2*n+1)*f(eta)*(diff(f(eta), eta, eta))/(2*n+2) = -n*(diff(f(eta), eta, eta))^(n-1)*(diff(f(eta), eta, eta, eta))+theta(eta)

(1/2)*(diff(f(eta), eta))^2-(2*n+1)*f(eta)*(diff(diff(f(eta), eta), eta))/(2*n+2) = -n*(diff(diff(f(eta), eta), eta))^(n-1)*(diff(diff(diff(f(eta), eta), eta), eta))+theta(eta)

 (3)
> 

indets(equ1);

{Pr, eta, n, Pr^(2/(n+1)), diff(diff(theta(eta), eta), eta), diff(theta(eta), eta), f(eta), theta(eta)}

  

{eta, n, (diff(diff(f(eta), eta), eta))^(n-1), diff(diff(diff(f(eta), eta), eta), eta), diff(diff(f(eta), eta), eta), diff(f(eta), eta), f(eta), theta(eta)}

 (4)
> 

Bcs := f(0) = 0, (D(f))(0) = 0, (D(f))(inf) = 1, theta(0) = 1, theta(inf) = 0;

f(0) = 0, (D(f))(0) = 0, (D(f))(9) = 1, theta(0) = 1, theta(9) = 0

  

1.301763965

  

1.4

 (5)
> 

equ1;

.7916666666666667*f(eta)*(diff(theta(eta), eta)) = .8027059130737796*(diff(diff(theta(eta), eta), eta))

  

(1/2)*(diff(f(eta), eta))^2-.7916666666666667*f(eta)*(diff(diff(f(eta), eta), eta)) = -1.4*(diff(diff(f(eta), eta), eta))^.4*(diff(diff(diff(f(eta), eta), eta), eta))+theta(eta)

 (6)
> 

SolP1 := dsolve({Bcs, equ1, equ2}, numeric); SolP1(0); SolP1(inf)

Error, (in dsolve/numeric/BVPSolve) unable to store '-.4744942626692375+1.460343180701223*I' when datatype=sfloat

  

SolP1(0)

  

SolP1(9)

 (7)
> 

p1 := plots:-odeplot(SolP1, [eta, f(eta)], 0 .. inf); p2 := plots:-odeplot(SolP1, [eta, theta(eta)], 0 .. inf); p3 := plots:-odeplot(SolP1, [eta, diff(f(eta), eta)], 0 .. inf); plots:-display(Array([p1, p2, p3]))

Error, (in plots/odeplot) input is not a valid dsolve/numeric solution

  

Error, (in plots/odeplot) input is not a valid dsolve/numeric solution

  

Error, (in plots/odeplot) input is not a valid dsolve/numeric solution

  

Error, (in plots:-display) element 1 of the rtable is not a valid plot structure

  
> 

``


 

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