ODE solver: Undefined function or variable 'y'?

2017 5 15
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更新时间：2017 5 15
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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?

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Star Strider
Star Strider 2017-5-15

0 个投票

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.

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