HP Forums
Solve System of differential equations - Printable Version

+- HP Forums (https://www.hpmuseum.org/forum)
+-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html)
+--- Forum: HP Prime (/forum-5.html)
+--- Thread: Solve System of differential equations (/thread-12076.html)



Solve System of differential equations - PepePepe - 01-03-2019 09:09 AM

How can I solve a system of differential equations in the HP Prime? Something like this:

x1'=x1+2*x2
x2'=3*x1+2*x2

I've tried to use desolve, but it seems it only works for one differential equation.

Thanks!


RE: Solve System of differential equations - parisse - 01-03-2019 12:44 PM

desolve(y'=[[1,2],[3,2]]*y,t,y)


RE: Solve System of differential equations - PepePepe - 01-03-2019 07:39 PM

But it seems that HP Prime it's doing something wrong if I do that. For example:

desolve(y'=[[1,0],[0,2]]*y,t,y)

gives the same solution as

desolve(y'=[[1,0],[0,2]]*y + [[3],[4]] ,t,y)

I think it is because the calculator is interpreting [[1,0],[0,2]]*y as [[y,0],[0,2y]] (it doesn't take into account that y is a vector)

How could I solve this? Am I doing something wrong?

Thanks!


RE: Solve System of differential equations - parisse - 01-05-2019 08:47 PM

Correct syntax for second member is
s:=desolve(y'=[[1,0],[0,2]]*y + [3,4] ,t,y)
The reason is that y is a line vector, not a column vector. Indeed desolve returns a list of generic solutions, even for linear ODE, because you might get several generic solutions for non linear ODE. That mean that the solution y is s[0], i.e. a line vector.