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Matlab expressing derivatives in an equation with ode45? 
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#1
Sep1910, 07:39 PM

P: 2

1. The problem statement, all variables and given/known data
(1)^4*xdx + (8yy^213)dy=0; y(0)=4; 1. Use dsolve to obtain a solution. 2. As dsolve was not much help find 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*yy^313)*Dy=0', 'y(0)=4') and got a huge matrixtype 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*yy^313)*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 


#2
Sep2010, 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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