Error using horzcat CAT arguments dimensions are not consistent

Hello everyone,

I have a M-file that I am going to invoke in another M-file to solve an ordinary differential equation. The file I am having trouble with is setting up the ODE to be solved. Here is the code:

function dy = dydtsys(tspan,y)

% given properties
g = 9.81; % acceleration due to gravity
l = 0.50; % length of each segment
p = 6500; % density of each segment
b = .05; % dimension of square cross section
m = l*(b*b)*p; % mass
Ic = m*l*l/12; % moment of inertia
theta1 = y(1); % angle of slider one
thetad1 = y(2); % angular velocity of slider one
theta2 = y(3); % angle of slider two
thetad2 = y(4); % angular velocity of slider two
xdd = @(tspan)((-4.2/2)*sin(4.2*tspan)); % slider acceleration

% Set up matrix A and vector b
A = [(Ic+((5/4)*m*(l^2))) ((1/2)*m*(l^2)*(cos(theta1-theta2)));...
    ((1/2)*m*(l^2)*(cos(theta1-theta2))) (Ic + ((1/4)*m*l*l))];
b = @(tspan) -[(((3/2)*m*(l*xdd(tspan))*(cos(theta1)))+((1/2)*(m*l*l)*   (sin(theta1-theta2))*...
    (thetad2.^2))+((3/2)*(m*g*l)*(sin(theta1))));...
    (((1/2)*(m*l*xdd(tspan))*(cos(theta2)))-((1/2)*(m*l*l)*(sin(theta1-theta2))...
    *(thetad1.^2))+((1/2)*(m*g*l)*(sin(theta2))))];
% A and b are the equations of motion based on Newton's second law

thetadd = @(tspan) A\b(tspan); % angular acceleration of each link

dy = [y(2) thetadd(1) y(4) thetadd(2)]';

end

The error is occuring in line 29:

dy = [y(2) thetadd(1) y(4) thetadd(2)]';

Any help is greatly appreciated! Thank you for your time,

Lia

[Matt Kindig]

This is strange, since anyvector(1) should return only one element.

Try this: assign thetadd(1) to a variable (e.g., "t1"). What is the size() and class() of t1?