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+--- Thread: how to solve a system of diff eq ? (/thread-6183.html)
how to solve a system of diff eq ? - hpfx - 05-01-2016 09:14 AM
Hello,
I try to solve this small system of differential equation :
x'(t)+y(t)=t^2
x'(t)+y'(t)=6
with initial conds : x(0)=0 and y(0)=1
I tried with desolve on 10077,
something like that desolve({x'+y=t^2, x'+y'=6} and x(0)=0 and y(0)=1, {x,y})
but I didn't get any result.
does someone knows how to do ?
RE: how to solve a system of diff eq ? - roadrunner - 05-01-2016 10:30 AM
Three points:
1. I solved the second equation for x', plug it into the first equation, and solved for x and y separately;
2. I think you have to tell desolve that t is the time variable or it assumes x;
3. I have never had luck typing y'. Typing diff(y) seems to work better.
Here's the code:
desolve(((6-(y')+y) = (t^2)) AND ((y(0)) = 1),t,y)
returns y:
t^2+5*e^t+2*t-4
diff(t^2+5*e^t+2*t-4,t)
returns y':
5*e^t+2*t+2
desolve(((x'+5*e^t+2*t+2) = 6) AND ((x(0)) = 0),t,x)
returns x:
-t^2-5*e^t+4*t+5
RE: how to solve a system of diff eq ? - parisse - 05-01-2016 11:39 AM
desolve solves differential equations, not systems, except for linear systems with constant coefficient for the homogeneous part, then the syntax is
desolve(y'=A*y+b) where A is the matrix and b a vector (second member)