how to solve a system of diff eq ?

05012016, 09:14 AM
Post: #1




how to solve a system of diff eq ?
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 ? 

05012016, 10:30 AM
Post: #2




RE: how to solve a system of diff eq ?
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*t4 diff(t^2+5*e^t+2*t4,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^25*e^t+4*t+5 

05012016, 11:39 AM
Post: #3




RE: how to solve a system of diff eq ?
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) 

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