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Matlab- expressing derivatives in an equation with ode45?

by Dsab123
Tags: matlab, ode45
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Dsab123
#1
Sep19-10, 07:39 PM
P: 2
1. The problem statement, all variables and given/known data

(-1)^4*xdx + (8y-y^2-13)dy=0; y(0)=4;
1. Use dsolve to obtain a solution.
2. As dsolve was not much help fi nd an implicit solution of the form
f(x, y) = 4

2. Relevant equations

---

3. The attempt at a solution

the dsolve part was easy, i just did:

syms x y t
dsolve('(-1^4)*x*Dx+(8*y-y^3-13)*Dy=0', 'y(0)=4')
and got a huge matrix-type answer.

So now, i'm having some trouble with 2. My prof told us to use ode45, and this is what i'm thinking:

Z='(-1^4)*x*Dx+(8*y-y^3-13)*Dy=0'
[x,y]=ode45(Z, -10:10, 4)

but i'm getting some errors that its not a proper function name, and some stuff with feval.
Is the problem with the Dy and Dx? My prof suggested using inline, but i read that its older syntax that doesn't really help much, according to mathworks :/

Any suggestions? thanks!
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution
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JeSuisConf
#2
Sep20-10, 06:29 PM
P: 34
ode45 (and all the other FD solvers in matlab) need you to provide it with a function that evaluates the differential equation at a given point. For example, check out function handles.


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