problem in creating function file using ode45

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Susmita Panda
Susmita Panda 2023-3-10
编辑： Torsten 2023-3-12
I am trying to solve a second order coupled ode using ode45, however I am facing issues in making it function file and providing variables as input. How to convert symbolic input to numerical in main file using ode45.

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采纳的回答

Torsten
Torsten 2023-3-11
编辑：Torsten 2023-3-11
Ran in:
Be careful with the order of the solution vector Y. It is (y, Dy, x, Dx). You have to supply the vector of initial values "ic" in the same order !
rng("default")
clc
clear all
close all
O=rand;
a=rand;
g=9.81;
L=rand;
[y]=coupled_ode(O, a, g, L);
VF = 
Subs = 
ftotal = function_handle with value:
@(t,Y)[Y(2);Y(1).*(-7.725211393067794e+1)-sin(9.057919370756192e-1).*Y(4).*1.629447372786358;Y(4);Y(3).*(-7.725211393067794e+1)+sin(9.057919370756192e-1).*Y(2).*1.629447372786358]
Disp=y;
function [y] = coupled_ode(Onum, anum, gnum, Lnum)
syms O a g L x(t) y(t) t Y
dx = diff(x);
d2x = diff(x,2);
dy = diff(y);
d2y = diff(y,2);
Eq1 = d2x == 2*O*sin(a)*dy - (g/L)*x(t);
Eq2 = d2y == -2*O*sin(a)*dx - (g/L)*y(t);
[VF,Subs] = odeToVectorField(Eq1, Eq2)
VF = subs(VF,[O a g L],[Onum anum gnum Lnum]);
ftotal = matlabFunction(VF,'Vars',{t,Y})
tspan = [0 25]; % Choose Appropriate Simulation Time
ic = [0 1 0 1]; % Choose Appropriate Initial Conditions
[t,y] = ode45(ftotal, tspan, ic);
figure
plot(t, y)
grid
legend(string(Subs))
end
  2 个评论
Susmita Panda
Susmita Panda 2023-3-12
Thank you @ Torsten sir. rng(default) helped me.This is exactly what I was searching.I didnt have any idea about this command.
Torsten
Torsten 2023-3-12
编辑：Torsten 2023-3-12
Ran in:
It's always a good idea if programming parts that serve different tasks have their own subfunctions. But in your case, I don't understand why and how you divided your code in the two different .m files.
E.g. to have control over what is done in the function coupled_ode, you will have to pass tspan, the initial conditions for the variables and the parameter values for O, a, g and L. The values returned should be t and y. The plotting part also should be done in the main program because it makes no sense to do the plotting in coupled_ode while passing the results as output parameters back to the calling program.
I'd arrange the code as
rng("default")
clc
clear all
close all
O = rand;
a = rand;
g = 9.81;
L = rand;
f = function_to_integrate(O, a, g, L)
f = function_handle with value:
@(t,Y)[Y(2);Y(1).*(-7.725211393067794e+1)-sin(9.057919370756192e-1).*Y(4).*1.629447372786358;Y(4);Y(3).*(-7.725211393067794e+1)+sin(9.057919370756192e-1).*Y(2).*1.629447372786358]
tstart = 0.0;
tend = 25.0;
tspan = linspace(tstart,tend,100); % Choose Appropriate Simulation Time
ic = [0 1 0 1]; % Choose Appropriate Initial Conditions
[t,y] = ode45(f, tspan, ic);
figure
plot(t, y)
grid
legend(string(Subs))
Unrecognized function or variable 'Subs'.
function f = function_to_integrate(Onum, anum, gnum, Lnum)
syms O a g L x(t) y(t) t Y
dx = diff(x);
d2x = diff(x,2);
dy = diff(y);
d2y = diff(y,2);
Eq1 = d2x == 2*O*sin(a)*dy - (g/L)*x(t);
Eq2 = d2y == -2*O*sin(a)*dx - (g/L)*y(t);
[VF,Subs] = odeToVectorField(Eq1, Eq2);
VF = subs(VF,[O a g L],[Onum anum gnum Lnum]);
f = matlabFunction(VF,'Vars',{t,Y});
end

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更多回答（1 个）

Alan Stevens
Alan Stevens 2023-3-10
Ran in:
Are you looking for something like this? (I might have misinterpreted your equations!)
O=1;
a=pi/2;
g=9.81;
L=100;
tspan = [0 15]; % Choose Appropriate Simulation Time
ic = [0 1 0 1]; % Choose Appropriate Initial Conditions
[t,y] = ode45(@(t,y) ftotal(t,y,O,a,g,L), tspan, ic);
figure
plot(t, y)
grid
legend('y1','dy1/dt','y2','dy2/dt')
function dydt=ftotal(~,y,O, a, g, L)
y1 = y(1); v1 = y(2); y2 = y(3); v2 = y(4);
dydt = [ v1;
2*O*sin(a)*y2 - g/L;
v2;
-2*O*sin(a) - g/L*y1];
end
  6 个评论
显示 4更早的评论
Susmita Panda
Susmita Panda 2023-3-11
Thank you @Torsten sir for this method. I will try this.
but is there any way we can call function "coupled_ode" in "Main_file" which I posted without error. This method is convenient to me and produces good result when they variables are called in same file.I am getting error of this kind when I am making it function file and providing variables in "Main_file":
Error using superiorfloat
Inputs must be floats, namely single or double.
Error in odearguments (line 114)
dataType = superiorfloat(t0,y0,f0);
Error in ode45 (line 107)
odearguments(odeIsFuncHandle,odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);
Error in coupled_ode (line 18)
[t,y] = ode45(@(t,y) ftotal(t,y,O,a,g,L), tspan, ic);
Error in Main_file (line 9)
[y]=coupled_ode(O, a, g, L);
Walter Roberson
Walter Roberson 2023-3-12
After you get the xddot and yddot using solve(), call odeFunction to create something to pass to ode45() .
I recommend following the workflow shown in the first example to odeFunction

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