ODE 45 Extra parameter

7 次查看（过去 30 天）
See Goo
See Goo 2022-8-23
回答： Torsten 2022-8-23
Hello
I hope you're well.
I am currently trying to plot with ODE45. This is a linear growth model.
My formula is (r*p*(1-p/N)) - ((200/2)*(1+sin(2*pi*t)/12))
ODE45 works fine when solving with just the first part of the formula
sol = ode45(@(t,p) (r*p*(1-p/N)) , tspan, p0);
however I am not sure how to implement the extra bit of code. I tried the following
sol = ode45(@(t,p) (r*p*(1-p/N)) - ((200/2)*(1+sin(2*pi*t)/12)), tspan,p0);
But dont think this is correct.
I'm not sure how to implement this extra bit. Would appreciate any help.
Thanks.
Kind regards,
  3 个评论
显示 1更早的评论
Steven Lord
Steven Lord 2022-8-23
Is there something in particular that leads you to doubt the answer you receive when you run your code? If so can you show us your code and explain your doubt in more detail?
See Goo
See Goo 2022-8-23
编辑：See Goo 2022-8-23
Thank you for the responses.
I am asked to run only for 15 instances, which represent 15 years.
The first and second case look identical except for after the 15 years time frame where i see some sinusoidal activity.
%Q1
tspan = [0 15];
p0 = 1000 + 1000*2;
r = 0.25;
N =20000;
ode = ode45(@(t,p) r*p*(1-p/N), tspan,p0);
t = linspace(0,15);
devals = deval(ode,t);
plot(t,devals);
xlabel('t');
ylabel('p');
%Q2
tspan = [0 15];
p0 = 1000 + 1000*2;
r = 0.25;
N =20000;
ode = ode45(@(t,p) r*p*(1-p/N) - ((200/2)*(1+sin(2*pi*t)/12)), tspan,p0);
t = linspace(0,15);
devals = deval(ode,t);
plot(t,devals);
xlabel('t');
ylabel('p');

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Torsten
Torsten 2022-8-23
Ran in:
I think there is quite a noticable difference between the solution curves.
%Q1
tspan = [0 15];
a = 1000 + 1000*2;
r = 0.25;
N =20000;
options = odeset('RelTol',1e-12,'AbsTol',1e-12);
[t,ode] = ode45(@(t,p) r*p*(1-p/N), tspan,a,options);
plot(t,ode)
hold on
%t = linspace(0,15);
%devals = deval(ode,t);
%plot(t,devals);
%xlabel('t');
%ylabel('p');
%Q2
tspan = [0 15];
a = 1000 + 1000*2;
r = 0.25;
N =20000;
[t,ode] = ode45(@(t,p) r*p*(1-p/N) - ((200/2)*(1+sin(2*pi*t)/12)), tspan,a,options);
plot(t,ode)
hold off
%t = linspace(0,15);
%devals = deval(ode,t);
%plot(t,devals);
xlabel('t');
ylabel('p');

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Ordinary Differential Equations 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by