Help! Trouble understanding differential equation.
显示 更早的评论
Hi my name is Hidde and i am a first year IEM student,
I got an assignment where i have to solve a differential equation written in the form: f'(t) = A*(g(t) - f(t)) + B*(h(t) - f(t))
I have never seen a DE with multiple functions inside it. I have data for the g(t) where all the values for g(t) are given in the interval [1, 1440] (with steps of 1).
h(t) is discribed as: h'(t) = C*(f(t) - h(t)) + C*(g(t) - h(t)).
i have to use ode45 to solve this problem.
5 个评论
Star Strider
2019-10-24
See the documentation on Function Basics if you have not already encountered functions, and the documentation on Anonymous Functions. Then review the documentation on ode45 or whatever solver you believe is necessary. Code the problem you want to solve. If you have problems, post back here. We can help you get your code running.
Hidde Kemperink
2019-10-24
Hidde Kemperink
2019-10-24
编辑：Hidde Kemperink
2019-10-24
John D'Errico
2019-10-24
You have never seen a differential equation with multiple functions in it? Surely not true. For example, something as simple as this:
y' = x + x^2
or
y' = exp(x) + x
would fit that goal.
Hidde Kemperink
2019-10-24
采纳的回答
Cyrus Tirband
2019-10-24
编辑：Cyrus Tirband
2019-10-24
Your differential equation is time-dependent, with given g(t). Ode45 works iteratively, and calls the function more than once with different values of t. You have to therefore interpolate your g(t) to the given times.
Further, notice that your differential equations can be written as
, where 
Knowing this, your ode function then becomes:
function dxdt = odefunc(t,x,g,gt,A,B,C)
f = x(1,:);
h = x(2,:);
g = interp1(gt,g,t); % Interpolate the data set (gt,g) at time t
dxdt(1,:) = B*h+A*g-(B+A)*f;
dxdt(2,:) = C*f+C*g-2*C*h;
end
Which can be directly fed to ode45 with the appropriate function handle, time span, and initial conditions.
5 个评论
Hidde Kemperink
2019-10-24
Cyrus Tirband
2019-10-24
I don't see how it is different. You are given T_amb, your time-dependent parameter, and you have a bunch of constants pertaining T_int and T_wall. The implementation is the exact same. You are also given the time frame and the initial conditions, so ode45 can umabiguously solve the set of equations.
Hidde Kemperink
2019-10-24
Cyrus Tirband
2019-10-24
It is almost the exact same. Just change the constants so that they correspond to to the constants of your problem. Completing this assignment should come with at the very least this rudimentary understanding.
Then, call the ode45 using the function you made and the appropriate other parameters. Check out the mathworks page on ode45 to acquaint yourself with its use. You won't need anything more than what's on that page.
Good luck with your assignment.
Hidde Kemperink
2019-10-24
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Programming 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
