ODE: equation solution problem

Hi everyone!

I'm using ode solvers for the first time, and I have some problems. I want to resolve y'(x) + 3 y(x) - 6x = 0, I use this code:

f = inline(' 6*x - 3*y');
[x,y] = ode45(f,[0 2],0);
plot(x,y)

obtaining correct result. Now I want to resolve y'(x) + 3 y(x) = 0. I wrote:

f = inline('- 3*y');
[x,y] = ode45(f,[0 2],0);
plot(x,y)

but there are errors:

"Error using inline/feval (line 25)
Too many inputs to inline function.
Error in odearguments (line 88)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.
Error in ode45 (line 114)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...]"

The same if I try to resolve y'(x) + 3y(x) = 2. How can I resolve this?

Thanks in advance.

Pinco

Answer 1

[Matt Tearle]

The problem is that the ODE solvers expect a function of two variables (x & y, in your case), but there's only one variable name in your second function. So one solution is to fake it:

f = inline('0*x-3*y');

But a better approach is to use function handles instead of inline:

f = @(x,y) 6*x - 3*y;

or

f = @(x,y) -3*y;

[Pinco]

Thanks so much!! It works perfectly!! :D :D