MATLAB code to find unknown parameters in ODEs using LM method

3 次查看（过去 30 天）
nado
nado 2022-10-14
编辑： nado 2022-10-14
Hello, I am trying to write a code for solving system of linear ODE with unknown parameters that need to fit the experimental data. I tried doing it by using this:
https://fr.mathworks.com/matlabcentral/answers/160452-matlab-code-for-solving-system-of-ode-with-unknown-parameters
But it didn't work. Or maybe I didn't do it properly because I didn't really understand what was what and how the variables were defined. My problem is:
[M]x_double_dot + [C]x_dot + [K]x = {0};
The experimental data is called "exp_open". I won't show exp_open here because it contains 15001 samples. I don't know if i did a mistake when writing the system in a state space form in order to use ode45.
The code i write is the same as : https://fr.mathworks.com/matlabcentral/answers/160452-matlab-code-for-solving-system-of-ode-with-unknown-parameters
But i obtain an error that said y and exp_open has not the same dimension.
Thank u for your help.
Here is my code :
km11=5.44e+5;
km15=-4.85e+7;
km55=-2073095808.81460221;
km51=-4.85e+7;
km0(1)=km11;
km0(2)=km15;
km0(3)=km55;
km0(4)=km51;
km_estimate=lsqnonlin(@(km)odefit_lm(t,exp_open,km),km0);
function [ err ] = odefit_lm( t,exp_open,km )
time=0:0.1:1500;
km11=km(1);
km15=km(2);
km55=km(3);
km51=km(4);
y0=[0;pi/18;0;0;0;0];
[t,y]=ode45(@(t,y)f_lm(t,y,km11,km15,km55,km51),time,y0);
err=y-exp_open;
end
function [dydt] = f_lm( t,y,km11,km15,km55,km51 )
M(1,1)=8.3163e+7;
M(1,2)=-2.6982e+9;
M(1,3)=1.8107e+6;
M(2,2)=5.6542e+11;
M(2,3)=3.4131e+8;
M(3,3)=1.4249e+6;
M(2,1)=M(1,2);
M(3,1)=M(1,3);
M(3,2)=M(2,3);
K(1,1)=km11;
K(1,2)=km15;
K(1,3)=0;
K(2,1)=km51;
K(2,2)=1.4604e+10+km55;
K(2,3)=0;
K(3,1)=0;
K(3,2)=0;
K(3,3)=1.4249e+6;
C(1,1)=1.8448e+5;
C(2,2)=1.8286e+10;
C(3,3)=4.0008e+10;
C(1,2)=5.8081e+7;
C(1,3)=-8.5911e+7;
C(2,3)=-2.7048e+10;
C(2,1)=C(1,2);
C(3,1)=C(1,3);
C(3,2)=C(2,3);
dydt(1)= y(4);
dydt(2)=y(5);
dydt(3)=y(6);
dydt(4:6)=-(M^(-1))*K*y(1:3)-(M^(-1))*C*y(4:6);
dydt=dydt';
end
In fact, i made some modifications to the code and i obtained another error:
Attempted to access y(5); index out of bounds because numel(y)=4.
Error in f_lm (line 49)
dydt(2)=y(5);
Error in odefit_lm>@(t,y)f_lm(t,y,km) (line 3)
[t,y]=ode45(@(t,y)f_lm(t,y,km),time,[5.44e+5 -4.85e+7 -2073095808.81460221 -4.85e+7]);
Error in odearguments (line 87)
f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.
Error in ode45 (line 113)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...
Error in odefit_lm (line 3)
[t,y]=ode45(@(t,y)f_lm(t,y,km),time,[5.44e+5 -4.85e+7 -2073095808.81460221 -4.85e+7]);
Error in @(km)odefit_lm(time,exp_y,km)
Error in lsqnonlin (line 194)
initVals.F = feval(funfcn{3},xCurrent,varargin{:});
Error in test_lm (line 45023)
km_estimate=lsqnonlin(@(km)odefit_lm(time,exp_y,km),km0);
Caused by:
Failure in initial user-supplied objective function evaluation. LSQNONLIN cannot continue.
  1 个评论
Jan
Jan 2022-10-14
Please post a copy of the complete error message. The details matter and it is not efficient to guess them.

请先登录，再进行评论。

请先登录，再回答此问题。

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