Matlab:解与条件不工作

Question

我正在试着解由变量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，只运行:

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

则一切正常，我得到:

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，我得到以下警告:

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。我错过了什么?如何以正确的方式指定条件，从而得到可绘图的结果?

Answer 1

您可以直接使用subs

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