Change parameter value during ode15s solution

1 次查看（过去 30 天）
gorilla3
gorilla3 2018-8-23
评论： gorilla3 2018-8-23
Hi,
I'm solving a set of differential equations and I'd like to change the value of a constant (Pin) at a specific time during the solution. Meaning that during the timespan, I'd like to change the value of Pin. So it time>10, Pin=70, else Pin=60.
This is how I formulated it but it's not working:
tspan=0:0.1:100;
cond= [...];
[t,y] = ode15s(@fun2,tspan, cond,[]);
function dydt= fun2(t,y)
for i=1:1:length(tspan)
if tspan(i)<10
Pin=60;
else
Pin=70;
end
end
...
end

请先登录，再回答此问题。

采纳的回答

Torsten
Torsten 2018-8-23
function dydt= fun2(t,y)
...
if t<10
Pin=60;
else
Pin=70;
end
...
Better use the EVENT-facility of the ODE solvers than the if-construction.
Best wishes
Torsten.
  3 个评论
显示 1更早的评论
Steven Lord
Steven Lord 2018-8-23
In this case I wouldn't use the events functionality. I tend to recommend that when you don't know at write-time when the events you're looking for will occur. In this case, you know exactly when it will occur: at t = 10.
Therefore I'd solve this problem twice. The first call to ode15s would solve from t = 0 to t = 10. I'd use the final result of that call to generate the initial conditions for the second call to ode15s, running from t = 10 to t = 100. Doing so would be easier with a slightly different function signature:
function dydt= fun2(t,y,Pin)
and specifying an anonymous function as the ODE function.
@(t, y) fun2(t, y, desiredValueOfPinForThisOde15sCall)
Replace desiredValueOfPinForThisOde15sCall with 60 or 70 depending on whether you're passing this anonymous function into the first or second ode15s call.
gorilla3
gorilla3 2018-8-23
thanks for the suggestion but this gives me an "instantaneous" response. Meaning that the solutions for (Pin=60, t<10) and (Pin=70, t>10) are just joined together but there's no information on the transition / adaptation of the system to this change. (see fig instant.jpg)
If, instead, I solve it all in one go, using the if-else within the function I can see the transition yet it's a linear jump. What I meant with my initial question is: is there a way to get more data points so that the plot would be a curve rather than these coarse lines? Indeed, the ode15s solver provides me only with 44 solution points, despite the tspan being of 1001. (see fig 10sreponse.jpg)

请先登录，再进行评论。

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