ODE solver: Undefined function or variable 'y'?

I'm attempting to find the intersection of two ODEs. I use the exact code provided here , but using different ODEs:

syms u(t) v(t)

ode1 = diff(x) == 0.25*x - 0.002*x.^2 - 0.005*x*y;
ode2 = diff(y) == 0.05*y - 0.009*y.^2 - 0.005*x*y;

odes = [ode1; ode2]

S = dsolve(odes)

xSol(t) = S.x
ySol(t) = S.y

[xSol(t), ySol(t)] = dsolve(odes)

cond1 = x(0) == 0.4184;
cond2 = y(0) == 0.6315;
conds = [cond1; cond2];
[xSol(t), ySol(t)] = dsolve(odes,conds)

fplot(xSol)
hold on
fplot(ySol)
grid on
legend('xSol','ySol','Location','best')

I get the following error:

Undefined function or variable 'y'. _ Error in final_2 (line 3) ode1 = diff(x) == 0.25*x - 0.002*x.^2 - 0.005*x*y;

Any help?

Answer 1

[Star Strider]

The problem is here:

syms u(t) v(t)

ode1 = diff(x) == 0.25*x - 0.002*x.^2 - 0.005*x*y;
ode2 = diff(y) == 0.05*y - 0.009*y.^2 - 0.005*x*y;

You need to re-define ‘ode1’ and ‘ode2’ in terms of ‘u’ and ‘v’. The Symbolic Math Toolbox requires that the variables be declared first, before you use them in your code.