Particular solution of a system of second order ODE \(\begin{bmatrix}-k &

Paula Boyer

Paula Boyer

Answered question

2022-04-22

Particular solution of a system of second order ODE
[kkkk][x1(t)x2(t)]+[Fk×ak×a]
=d2dt2[x1(t)x2(t)]

Answer & Explanation

gonzakunti2

gonzakunti2

Beginner2022-04-23Added 16 answers

Step 1
I will write your system as
x=Mx+b,
where xR2,,
M=(kkkk),
and
b=(Fk×ak×a)
assuming that × is multiplication of scalars.
Now do a linear transformation to y=xM1b, giving that
y=My.
Then I believe this equation has solutions of the form
y(t)=y1exp(Nt)+y2exp(Nt),
where yiR2, exp is the matrix exponential, and N is any matrix square root of M, satisfying N2=M
It suffices to find square roots of your M, which may or may not exist, I didn't check.
Edit; I realised that your matrix is not invertible, so my solution doesn't work. I will leave it up in case this solution for invertible M is still useful for someone.
Annie Levine

Annie Levine

Beginner2022-04-24Added 15 answers

Step 1
Writing your system as
x=k(yx)+Fak,
and
y=k(xy)+ak,
leads me to change coordinates to u=x+y, v=xy, in which case your equations decouple to
u=F
and
v=2kv+F2ak.
I would expect both of these ODEs to be covered in a first course on differential equations. You can use the linear transformation that I used in my other answer to remove the constant term from the second equation.

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