How to solve symbolic ODE system

Forum|Forum|7 years ago
February 5, 2019
3 replies
2123 views

Hi everyone,

I'm trying to solve this EDO system, finding the solution for x(t) and p(t) with {k1,k2,b} symbolic variables and m=535:

System Equations:

m*x''(t)=-k1*(x(t)-p(t))-b*(x'(t)-p'(t))

k2*p(t)=k1*(x(t)-p(t))+b*(x'(t)-p'(t))

Initial Conditions would be:

x(0)=0

p(0)=0

x'(0)=6.3

Already tried with Wolfram Alpha and Matlab, both giving solutions with terms "Root[#1^3+ (k1 m + k2 m) #1^2 + b^2 k2 m #1 + b^2 k1 k2 m^2&, 1]" in which I don't understand what is represented. Examples attached in following pictures:

Matlab:

Calculus_Derivatives

W

Werner_E

25-Diamond I

Mathcad can solve ODEs only numerically, not symbolically.

The "Root" you see in the symbolic solutions of Matlab and Wolfram possibly is the solution of a cubic equation which cannot be given in a closed form as its form depends on the values of the various constants.

M

mvenich

14-Alexandrite

Seems like Maple will give an explicit solution without any Root's

Here's the commands

The full result in in the attached PDF

1_de.pdf

L

LucMeekes

23-Emerald IV

Here's how you could (try to) solve it:

So now we have X and P...

And that's where it becomes a little problematic. You have to take the inverse Laplace transform of a ratio of polynomes where the order of the denomonator polynome is 3. This is not easy, but apparently modern Maple can do it, as Mvenich shows. I've entered one of the two expressions in WolframAlpha, to find a similar expression involving the root() function: