answer different on MATLAB than the expected answer

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Hamzah Al-Hamidi
Hamzah Al-Hamidi on 16 Nov 2021
Commented: Paul on 16 Nov 2021
i have used this code to solve ODE
syms y(x)
Q_22= (diff(y,x,3))- (diff(y,x,2))== 6;
disp('The solution is:')
The solution is:
ySol(x) = simplify(dsolve(Q_22))
ySol(x) = 
But the expected answer i needed to be is as following :
these are the steps of solving it :

Accepted Answer

Paul
Paul on 16 Nov 2021
Mathematically, the answers are the same because the Ci are abitrary constants (absent any othe conditions on the solution). So the mapping from the Matlab solution to your solution is:
C1 + C2 - 6 -> C1
C1 - 6 -> C2
C3 -> C3
Or did you realize this and you just want to manipulate the Matlab solution to be in the same form as yours?
  2 Comments
Paul
Paul on 16 Nov 2021
If you know the answer you're going for, at least after seeing the form of ySol, you can manipulate manually
syms y(x)
Q_22= (diff(y,x,3))- (diff(y,x,2))== 6;
ySol(x) = simplify(dsolve(Q_22))
ySol(x) = 
syms C1 C2 C3 K1 K2 K3
ySol = subs(ySol,[C1+C2-6,C1-6,C3],[K1 K2 K3])
ySol(x) = 
ySol = subs(ySol,[K1 K2 K3],[C1 C2 C3])
ySol(x) = 
Automating this process would be more work, assuming it's even feasible.

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