Matrices in ODE function

I have this ODE Function where Mn, Kn, Kb, and Gamma are Matrices. ag is a ground motion records (attached txt file) , ts and ag have the same length. Attached the script, the Function, and the text file.

The Script

Gamma=[0.5637,0,0;0,0.3413,0;0,0,0.094];
Mn=[5443,0,0;0,1175,0;0,0,2105];
Kn=[3315304,0,0;2.0,547601,0;0,0,1968524];
Kb=[38013,0,0;0,19006,0;0,0,11404];
C_alpha_1=43180;
g=9.81;
ag=dlmread('ElCentro.txt');
ts=[0:0.01:40]';
IC = zeros(3);
[T, Y]=ode23s(@(t,y)fvdfn(t,y,ts,ag,g,Gamma,Mn,Kn,Kb,C_alpha_1),ts,IC);

The Function

function [ yp ] = fvdfn(t,y,ts,ag,g,Gamma,Mn,Kn,Kb,C_alpha_1)

agt=interp1(ts,ag,t);

X1=y(2);

X2=Gamma*agt*g+(Kn/Mn)*y(1)+y(3)./Mn;

X3=Kb*y(2)-Kb*y(3)/C_alpha_1;

yp=[X1; X2; X3];
end

Then I called this function inside the script, when I run the script I get an error that the dimensions of matrices being concatenated are not consistent. I expect to get a matrix of three columns for y(1), y(2), and y(3) with a length same as vector ag. Any help to get rid of this error.

[Walter Roberson]

You have X1 = y(2) which is a scalar. A scalar is not a vector of the same length as ag.

Note that if you did get out a length(ag) by 3 array that ode23s would reject it:

https://www.mathworks.com/help/matlab/ref/ode23s.html#bu5ypsh_sep_shared-odefun

The function dydt = odefun(t,y), for a scalar t and a column vector y, must return a column vector dydt of data type single or double that corresponds to f(t,y).

Answer 1

[Abraham Boayue]

I find it a bit odd to follow your system of equations, your derivities are given in x1, x2, and x3 and you are trying to find y1 , y2 and y3? Is this really correct? Can you post the equations as they were given instead?