Using ODE45 to Solve Matrix Differential Equations in MATLAB

  • Thread starter Thread starter madjid222
  • Start date Start date
  • Tags Tags
    Matlab Ode45
AI Thread Summary
To solve a system of matrix and scalar differential equations using MATLAB's ode45, the matrix variable must be reshaped appropriately. The example provided demonstrates how to set up the matrices A and Q, and how to define the ODE function that incorporates both matrix and scalar equations. The matrix X is reshaped from a column vector back into a 3x3 matrix within the ODE function, and the output dxdt is converted back into a column vector for ode45. The code snippet illustrates the process of defining the time span and plotting the results after solving the equations. Properly handling the dimensions of the variables is crucial for successful implementation.
madjid222
Messages
4
Reaction score
0

Homework Statement



If we have differential variable of matrix kind ( with dimention 3*3 ) and non matrix ( with dimention 1) simaltanously and as a couple ,how can we use ode45 ?
If we have only matrix kind , we can use m file of ode at first with the command of reshape (3,3) and then change it to column one.What is the solution in this case ?

Homework Equations


P,A,Q :matrices 3*3
Pdot= A*P +P*A’ +Q
K=P*[1 0 0]
xdot(1) =f(x(1),x(2),x(3)) +k(1)*x(1)
xdot(2)=g(x(1),x(2),x(3)) +k(2)*x(2)
xdot(3)=h(x(1) ,x(2),x(3)) +k(3)*x(3)
x0=[ xa;xb;xc]
P0=x01

The Attempt at a Solution


Example (only matrix differential equation) :
%-----MAIN M-FILE--------------
clear all
%-----VARIABLE SET-UP--------------

A = [0 1 0; 0 0 5; 1 2 3];
Q = [1 0 0; 0 0.5 0; 0 0 0.9];
%-----TO RUN and PLOT ODE SOLUTION--------------
t01= 0;
tf1=30;
tspan1 = LINSPACE(t01, tf1);
X01=zeros(3);
[Time1,X1] = ode45(@(t,X) odefuncare(t,X,A,Q),tspan1,X01);
plot(Time1,X1)
%-------ODEFUNCTION------------------
function dxdt = odefuncare(t,X,A,Q)
X = reshape(X,3,3); %converting X from a column vector generated by ode45 into a 5 x 5 Matrix
dxdt=A*x +x*A’ +Q
dxdt = dxdt(:); %converting dxdt into a column vector as expected by ode45
 
Last edited:
Physics news on Phys.org
I would be grateful if you could possibly help me
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Back
Top