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问题

原来微分方程里面还有一类比较特殊复杂的。delay differential equation(维基).
翻了几篇相关的硕士和博士论文，感觉用处不大。不过，用软件做出来效果比较漂亮。

与之相关的, 分支或分叉(bifurcation)是一个似乎在包括迭代的动力系统里面都普遍的一个概念。

Wolfram关于这个概念的文档

延迟微分方程是一种微分方程，其在当前时间的时间导数取决于它在以往时间的解，还可能取决于它在以往时间的导数：

目前，在 NDSolve 中延迟微分方程的实现只支持常量延迟.

虽然延迟微分方程看起来很像常微分方程，它们的理论更加复杂，并且与常微分方程有一些令人吃惊的不同之处

同样是数值计算，更愿意用mathematica而不是可能更强的matlab, 主要是演示效果吧。

Mathworks关于这个概念的文档

Matlab中Delay Differential Equations求解用到的函数
论文一篇：用Matlab解DDE(2001)：

No.	Delay differential equation initial value problem solvers	Functions
1	`dde23`	Solve delay differential equations (DDEs) with constant delays
2	`ddesd`	Solve delay differential equations (DDEs) with general delays
3	`ddensd`	Solve delay differential equations (DDEs) of neutral type
4	`ddeget`	Extract properties from delay differential equations options structure
5	`ddeset`	Create or alter delay differential equations options structure
6	`deval`	Evaluate solution of differential equation problem

一些演示

这里写图片描述

其它软件很少有这种特色的论坛：

First, I have a few general comments. The simplest bifurcation diagrams for differential equations involve a single parameter in a single equation and there are several illustrations of these on the Wolfram Demonstrations site. More generally, of course, a bifurcation occurs when we see a qualitative change in the behavior of a system as some parameter changes. For a system of equations, we could use the eigensystem of the linearization of the system in the neighborhood of an equilibrium to identify bifuractions. You, however, appear to have four differential-algebraic equations with 16 parameters. Also, a number of these (K, I, E, N) are actually reserved symbols; I’d avoid that.

I don’t think I’m going to wade into this system that I know nothing about but I can present some ideas to study this kind of thing in the context of an example that I understand, namely the Selkov model presented on the Demonstrations site:

That demonstration shows you how to study the bifurcation using NDSolve. It might make sense to study it using the groovy new ParametricNDSolve. First, the system is the following:
pf = ParametricNDSolveValue[{ x'[t] == -x[t] + a*y[t] + x[t]^2 y[t], y'[t] == b - a*y[t] - x[t]^2*y[t], x[0] == 0, y[0] == 2}, {x, y}, {t, 0, 100}, {a, b}];

We can investigate the behavior with respect to the parameters as follows. If you hold $a=0.1$ and let be range, a two Hopf bifurcations (changes from fixed point to cycle and back) should be evident

Manipulate[ Block[{$PerformanceGoal = "Quality"}, Show[{ ContourPlot[-x + a*y + x^2 y == 0, {x, 0, 3}, {y, 0, 3}, ContourStyle -> Dashed], ContourPlot[b - a*y - x^2*y == 0, {x, 0, 3}, {y, 0, 3}, ContourStyle -> Dashed], StreamPlot[{-x + a*y + x^2 y, b - a*y - x^2*y}, {x, 0, 3}, {y, 0, 3}, StreamStyle -> Directive[Opacity[0.5]]], ParametricPlot[ Evaluate[Through[pf[a, b][t]]], {t, 0, 100}, PlotRange -> { {0, 3}, {0, 3}}, PlotStyle -> Directive[Thickness[0.007], Black]]}]], { {a, 0.1}, 0, 1}, {b, 0, 1}]