Question

我正在尝试解决由变量eqn1和eqn2给出的微分方程组。

lambda1 = 3;
lambda2 = 2;
gamma1 = 1;
gamma2 = 1;
delta1 = 1;
delta2 = 1;

syms n1(t) n2(t)
eqn1 = diff(n1) == (lambda1 - gamma1)*n1 - delta1*(n1 + n2)*n1;
eqn2 = diff(n2) == (lambda2 - gamma2)*n2 - delta1*(n1 + n2)*n2;

c1 = n1(0) == 10;
c2 = n2(0) == 10;
[a, b] = dsolve(eqn1, eqn2, c1, c2)

如果我没有指定条件c1和c2并且只运行：

[a, b] = dsolve(eqn1, eqn2)

然后一切都很好，我得到了：

a =

(6*exp(2*t)*n1(0))/(3*exp(2*t)*n1(0) + 4*exp((3*t)/2)*n2(0) + 6)


b =

(6*exp(t/2)*exp(t)*n2(0))/(3*exp(2*t)*n1(0) + 4*exp((3*t)/2)*n2(0) + 6)

但是当我尝试指定n1（0）和n2（0）时，正如您在源代码中看到的那样，我收到以下警告：

a =

Warning: The result cannot be displayed due a previously interrupted     computation or out of memory. Run 'reset(symengine)' and rerun the commands to regenerate the result. 
> In sym.disp at 36
  In sym.display at 37
  In competingForResources at 15 

b =

     []

我无法绘制结果。我在那里错过了什么？如何以正确的方式指定条件，所以我得到了一个可绘制的结果？

Answer 1

您可以使用subs

直接替换结果中的值

[a, b] = dsolve(eqn1, eqn2);
a=subs(a,'n1(0)',10);
a=subs(a,'n2(0)',10)

a =

(60*exp(2*t))/(30*exp(2*t) + 40*exp((3*t)/2) + 6)

与b

相同

Matlab：dsolve条件不起作用

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