how I can fix sample time in ode45
显示 更早的评论
I want to fix the sample time (for example, T=0.5) in ode45. How can I do it? If it is not possible, do we have another way to fix the sample time in Matlab?
tspan = 0:1:10000;
y0 = [0.2,0.3];
[t,y] = ode45(@(t,y) odefcn(t,y), tspan, y0);
%
function dx = odefcn(t,x)
dx = zeros(2,1);
u=[2 -2]*x(1:2)+1;
dx(1)=x(1)-2*x(2)
dx(2)=-x(2)+u
end
采纳的回答
Are you looking for something like this?
T = 0.5;
tspan = 0:T:10;
y0 = [0.2,0.3];
[t, y] = ode45(@(t,y) odefcn(t,y), tspan, y0);
plot(t, y, '-o'), grid on
xlabel('Time')
%
function dx = odefcn(t,x)
dx = zeros(2,1);
u = [2 -2]*x(1:2) + 1;
dx(1) = x(1) - 2*x(2);
dx(2) = - x(2) + u;
end
3 个评论
hossen hassanzadth
2023-10-29
Indeed, ode45() solver employs its own internal steps for computing the solution and subsequently assesses the solution at the designated points in tspan. Nonetheless, it is crucial to emphasize that the solutions generated at the specified points exhibit the same level of accuracy as the solutions computed at each internal step. Another approach is to use deval().
tspan = [0, 10];
y0 = [0.2, 0.3];
sol = ode45(@(t,y) odefcn(t,y), tspan, y0);
T = 0.5;
t = 0:T:10;
y = deval(sol, t);
plot(t, y, '-o'), grid on
xlabel('Time')
function dx = odefcn(t,x)
dx = zeros(2,1);
u = [2 -2]*x(1:2) + 1;
dx(1) = x(1) - 2*x(2);
dx(2) = - x(2) + u;
end
Else everything fails, you can write a simple algorithm using the convetional Runge–Kutta solver that allows the fixed step size for the integration..
h = 0.5;
x = 0:h:10;
% Initial values
y(:,1) = [0.2 0.3];
% Input signal
u = @(y) [2 -2]*y + 1;
% State equations
odefcn = @(t, y) [y(1) - 2*y(2);
- y(2) + u(y)];
% Runge-Kutta ODE Solver
for i = 1:(length(x)-1)
k1 = odefcn(x(i), y(:,i));
k2 = odefcn(x(i)+0.5*h, y(:,i)+0.5*h*k1);
k3 = odefcn(x(i)+0.5*h, y(:,i)+0.5*h*k2);
k4 = odefcn(x(i)+h, y(:,i)+k3*h);
y(:,i+1) = y(:,i) + (h/6)*(k1 + 2*k2 + 2*k3 + k4);
end
plot(x, y, '-o'), grid on
xlabel('Time')
更多回答（1 个）
Walter Roberson
2023-10-29
0 个投票
You cannot do that. ode45() is always a variable-step solver. So is ode15s, ode23s, ode78, ode113, ode89.
If you need a fixed step solver then see https://www.mathworks.com/matlabcentral/answers/98293-is-there-a-fixed-step-ordinary-differential-equation-ode-solver-in-matlab-8-0-r2012b#answer_107643
类别
在 帮助中心 和 File Exchange 中查找有关 Ordinary Differential Equations 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 
