must return a column vector

I know this is a dimension issue, but i just can't see it at the moment. could someone help me out.

n=12;
x=zeros(1,2*n);
ct=zeros(n,n);
l=3; % in m
t=6;
%%%%%%%%%mass matrix %%%%%%%%%%%%%%
g=5000;
m=[ g,0,0,0,0,0,0,0,0,0,0,0;
    0,g,0,0,0,0,0,0,0,0,0,0;
    0,0,g,0,0,0,0,0,0,0,0,0;
    0,0,0,g,0,0,0,0,0,0,0,0;
    0,0,0,0,g,0,0,0,0,0,0,0;
    0,0,0,0,0,g,0,0,0,0,0,0;
    0,0,0,0,0,0,g,0,0,0,0,0;
    0,0,0,0,0,0,0,g,0,0,0,0;
    0,0,0,0,0,0,0,0,g,0,0,0;
    0,0,0,0,0,0,0,0,0,g,0,0;
    0,0,0,0,0,0,0,0,0,0,g,0;
    0,0,0,0,0,0,0,0,0,0,0,g];
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%Damping ratio matrix%%%%%%%
h=0.1;
zeta=[ h,0,0,0,0,0,0,0,0,0,0,0;
    0,h,0,0,0,0,0,0,0,0,0,0;
    0,0,h,0,0,0,0,0,0,0,0,0;
    0,0,0,h,0,0,0,0,0,0,0,0;
    0,0,0,0,h,0,0,0,0,0,0,0;
    0,0,0,0,0,h,0,0,0,0,0,0;
    0,0,0,0,0,0,h,0,0,0,0,0;
    0,0,0,0,0,0,0,h,0,0,0,0;
    0,0,0,0,0,0,0,0,h,0,0,0;
    0,0,0,0,0,0,0,0,0,h,0,0;
    0,0,0,0,0,0,0,0,0,0,h,0;
    0,0,0,0,0,0,0,0,0,0,0,h];
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%Stiffness matrix%%%%%%%%%%
b=4*((3*100)/l); %kN/m
k=[ 2*b,-b,0,0,0,0,0,0,0,0,0,0;
    -b,2*b,-b,0,0,0,0,0,0,0,0,0;
    0,-b,2*b,-b,0,0,0,0,0,0,0,0;
    0,0,-b,2*b,-b,0,0,0,0,0,0,0;
    0,0,0,-b,2*b,-b,0,0,0,0,0,0;
    0,0,0,0,-b,2*b,-b,0,0,0,0,0;
    0,0,0,0,0,-b,2*b,-b,0,0,0,0;
    0,0,0,0,0,0,-b,2*b,-b,0,0,0;
    0,0,0,0,0,0,0,-b,2*b,-b,0,0;
    0,0,0,0,0,0,0,0,-b,2*b,-b,0;
    0,0,0,0,0,0,0,0,0,-b,2*b,-b;
    0,0,0,0,0,0,0,0,0,0,-b,2*b];
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
a=m^(-0.5);
kt=a*k*a;
[p,q]=eig(kt);
omega=sqrt(q);

for zt=1:n
 ct(zt,zt)=zeta(zt)*2*omega(zt,zt);
end
af=a^(-1);
c=af*ct*af;

v0=[0;0;0;0;0;0;0;0;0;0;0;0];%initial velocities
x0=[0;0;0;0;0;0;0;0;0;0;0;0];%initial displacement
ti=0;                        %initial time
tf=100;                      %final time
init=[v0,x0];                %initial velocity and displacement initialize    

[t,ny]=ode45(@yd,[ti,tf],init);

for kl=1:n
plot(t,ny(:,kl+n),'b');
title(['Response x',num2str(kl)]);
xlabel('Time, seconds');
ylabel('Displacement, m');
grid
figure(gcf)
pause
end

here is the file it references

if true
function yd=yd(t,x)
yd(1)=(-((800)*x(13)+(68.1858)*x(1)*(-400)*x(14))+(0))/(5000);
yd(2)=(-((-400)*x(13)*(800)*x(14)*(-400)*x(15))+(0))/(5000);
yd(3)=(-((-400)*x(14)*(800)*x(15)*(-400)*x(16))+(0))/(5000);
yd(4)=(-((-400)*x(15)*(800)*x(16)*(-400)*x(17))+(0))/(5000);
yd(5)=(-((-400)*x(16)*(800)*x(17)*(-400)*x(18))+(0))/(5000);
yd(6)=(-((-400)*x(17)*(800)*x(18)*(-400)*x(19))+(0))/(5000);
yd(7)=(-((-400)*x(18)*(800)*x(19)*(-400)*x(20))+(0))/(5000);
yd(8)=(-((-400)*x(19)*(800)*x(20)*(-400)*x(21))+(0))/(5000);
yd(9)=(-((-400)*x(20)*(800)*x(21)*(-400)*x(22))+(0))/(5000);
yd(10)=(-((-400)*x(21)*(800)*x(22)*(-400)*x(23))+(0))/(5000);
yd(11)=(-((-400)*x(22)*(800)*x(23)*(-400)*x(24))+(0))/(5000);
yd(12)=(-((-400)*x(23)*(800)*x(24))+(5000*sin(3*t)))/(5000);
yd(13)=x(1);
yd(14)=x(2);
yd(15)=x(3);
yd(16)=x(4);
yd(17)=x(5);
yd(18)=x(6);
yd(19)=x(7);
yd(20)=x(8);
yd(21)=x(9);
yd(22)=x(10);
yd(23)=x(11);
yd(24)=x(12);
end

Answer 1

[Star Strider]

I didn’t run your code, but see if making the first statement after the function statement a preallocation of ‘yd’ to be a column vector will help:

yd = zeros(24,1);

Also, it’s not good practice to name your function the same as the variables within it or the variable it returns. Change the function name to ‘ydf’ or something that is meaningful in the context of your code. Also change the name of the .m file containing it and of course the reference in ode45.

Answer 2

[ryan]

yup that got rid of all errors. thanks.

[Star Strider]

My pleasure!