can you please help me solve this diffetential equation system?

1 次查看（过去 30 天）
SOUGLES STAMATIS
SOUGLES STAMATIS 2021-4-7
评论： Alan Stevens 2021-4-8
I need to solve a differential system and I coded in this way . I doesn't seem to work. I want to solve it only for t [0,4]. how can i do that?
syms x1(t) x2(t) x3(t) x4(t) x5(t) x6(t)
b=4.2030*10^5
m=1.0508*10^6
k=3.5025*10^9
A = [-2*b/(3*m) b/(3*m) 0 1/(3*m) -1/(3*m) 0 ;
b/(2*m) -2*b/(2*m) b/(2*m) 0 1/(3*m) -1/(3*m) ;
0 b/m -b/m 0 0 1/m ;
-k 0 0 0 0 0 ;
k -k 0 0 0 0 ;
0 k -k 0 0 0];
B = [-b/(3*m)*(1.8747*log(t)+8.6905);
0;
0;
-k*(1.8747*log(t)+8.6905);
0;
0;];
Y = [x1; x2; x3; x4; x5; x6];
odes = diff(Y) == A*Y + B
C = Y(0) == [0;0;0;0;0;0];
[x1Sol(t), x2Sol(t), x3Sol(t), x4Sol(t), x5Sol(t), x6Sol(t)] = dsolve(odes,C);
x1Sol(t) = simplify(x1Sol(t))
x2Sol(t) = simplify(x2Sol(t))
x3Sol(t) = simplify(x3Sol(t))
x4Sol(t) = simplify(x4Sol(t))
x5Sol(t) = simplify(x5Sol(t))
x6Sol(t) = simplify(x6Sol(t))

请先登录，再回答此问题。

回答（1 个）

Alan Stevens
Alan Stevens 2021-4-7
You have log(t) in the definition of B. This causes problems at t = 0.
  2 个评论
Alan Stevens
Alan Stevens 2021-4-8
Like this
x0 = [0;0;0;0;0;0];
tspan = [0.01 4];
[t, x] = ode45(@bc, tspan, x0);
plot(t,x),grid
function xdot = bc(t,x)
b=4.2030*10^5;
m=1.0508*10^6;
k=3.5025*10^9;
A = [-2*b/(3*m) b/(3*m) 0 1/(3*m) -1/(3*m) 0 ;
b/(2*m) -2*b/(2*m) b/(2*m) 0 1/(3*m) -1/(3*m) ;
0 b/m -b/m 0 0 1/m ;
-k 0 0 0 0 0 ;
k -k 0 0 0 0 ;
0 k -k 0 0 0];
B = [-b/(3*m)*(1.8747*log(t)+8.6905);
0;
0;
-k*(1.8747*log(t)+8.6905);
0;
0;];
xdot = A*x + B;
end
You might need to plot the different x's on separate graphs to see them all properly.
Note that the results will be somewhat different depending on your starting value for t.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Ordinary Differential Equations 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by