Is there a better way of solving simultaneous differential equations then using dsolve as MATLAB crashes everytime I use it?

So I have a set of simulataneous differential equtions that need to be solved as such:

Ive been using this code but as stated in the title MATLAB crashes is there any better way of doing this:

clear
clc
syms P1(t) P2(t) P3(t) P4(t) P5(t) P6(t) P7(t) P8(t)...
    Lam1 Lam2 Lam3 Mu1 Mu2 Mu3



% Typing in all the equations
eqns = ...
   [diff(P1,t) == (-Lam1-Lam2-Lam3)*P1 + (Mu1)*P2 + (Mu2)*P3 + (Mu3)*P4,...
    diff(P2,t) == (Lam1)*P1 + (-Mu1-Lam2-Lam3)*P2 + (Mu2)*P5 + (Mu3)*P6,...
    diff(P3,t) == (Lam2)*P1 + (-Mu2-Lam1-Lam3)*P3 + (Mu1)*P5 + (Mu3)*P7,...
    diff(P4,t) == (Lam3)*P1 + (-Mu3-Lam1-Lam2)*P4 + (Mu1)*P6 + (Mu2)*P7,...
    diff(P5,t) == (Lam2)*P2 + (Lam1)*P3 + (-Mu1-Mu2-Lam3)*P5 + (Mu3)*P8,...
    diff(P6,t) == (Lam3)*P2 + (Lam1)*P4 + (-Mu1-Mu3-Lam2)*P6 + (Mu2)*P8,...
    diff(P7,t) == (Lam3)*P3 + (Lam2)*P4 + (-Mu2-Mu3-Lam1)*P7 + (Mu1)*P8,...
    diff(P8,t) == (Lam3)*P5 + (Lam2)*P6 + (Lam1)*P7 + (-Mu1-Mu2-Mu3)*P8]
  

% Solutions Solver
sol = dsolve(eqns, P1(0) == 1, P2(0) == 0, P3(0) == 0, P4(0) == 0,P5(0) == 0, P6(0) == 0,...
P7(0) == 0, P8(0) == 0)

% Printing the Solutions
solP1(t)= sol.P1
solP2(t)= sol.P2
solP3(t)= sol.P3
solP4(t)= sol.P4
solP5(t)= sol.P5
solP6(t)= sol.P6
solP7(t)= sol.P7
solP8(t)= sol.P8

[Stephan]

What do you mean with Matlab crashes? Which Release do you use? Are there values for lambda and/or mu?

[Benjamin Watson]

Hi Stephan,

When I say MATLAB crashes I mean it seems to get stuck solving as I had it trying to run for 6hrs without an output yesterday. I use 2016b and there are values for Lam and Mu but I want a sybollic output. Thanks, hope you can help.

Ben

[Walter Roberson]

For whatever it is worth, Maple returns a solution within a reasonable time. I have attached it as a file due to technical problems with copy/paste.

[Stephan]

?

Answer 1

[Star Strider]

You have a linear system:

so the solution is going to be the matrix exponential:

that in MATLAB code is:

syms P(t) Lam1 Lam2 Lam3 Mu1 Mu2 Mu3 t 

A = [ - Lam1 - Lam2 - Lam3,                 Mu1,                 Mu2,                 Mu3,                  0,                  0,                  0,                 0
                      Lam1, - Lam2 - Lam3 - Mu1,                   0,                   0,                Mu2,                Mu3,                  0,                 0
                      Lam2,                   0, - Lam1 - Lam3 - Mu2,                   0,                Mu1,                  0,                Mu3,                 0
                      Lam3,                   0,                   0, - Lam1 - Lam2 - Mu3,                  0,                Mu1,                Mu2,                 0
                         0,                Lam2,                Lam1,                   0, - Lam3 - Mu1 - Mu2,                  0,                  0,               Mu3
                         0,                Lam3,                   0,                Lam1,                  0, - Lam2 - Mu1 - Mu3,                  0,               Mu2
                         0,                   0,                Lam3,                Lam2,                  0,                  0, - Lam1 - Mu2 - Mu3,               Mu1
                         0,                   0,                   0,                   0,               Lam3,               Lam2,               Lam1, - Mu1 - Mu2 - Mu3];

P = expm(A*t)

My Ryzen 7 1700 machine has been working on this for the past hour and does not appear to be close to finishing. I’m stopping it now, and will let you pursue this.