Dimensions of array being concatenated are not consistent

Hi,

I'm trying to use the Central Difference method to do a strucutral analysis of a structure subjected to an earthquake. I should be getting the displacements for every time period with the acceleration but I keep getting the error " Dimensions of array being concatenated are not consistent". Can anyone help and see what I might be inputting incorrectly? I have my code below

clear all 
clc

EC=xlsread('KobeAT2H');  % Define Earthquake Motion
t=EC(:,1);   % Time Vector from El Centro GM Data
Ag=EC(:,2); % Acceleration vector from El Centro Data in/^sec^2
plot(t,Ag)
xlabel('Time (sec)')
ylabel('Acceleration (g) for El centro Earthquake')

% Parameters of Structure
dt=0.01;
g=386.4;     %Acceleration of Gravity in in/s^2
b=0.0775;   % Base length of Columns (inch)
h=12;   % Height of Columns in Each floor(inch)
E=29000; % Elastic Modulus of Structure (ksi) Steel
I=b*h^3/12;   % Second-Moment of Inertia of Columns (in^4)
ks=24*(E*I/h^3); %Stiffness Kip/in
M=13.8; % Total Mass of Steel Structure
Wn=sqrt(ks/M);  % Natural Frequency
c=2*M*0.02*Wn; %Damping 

% Central difference Method
p=-M*Ag; % Initial Force at time 0
uo=0; % Initial Displacement   
u1=0; %  Initial Velocity
udd=(p-c*u1-ks*uo)/M;
um1=uo-(dt)*u1+(dt)^2/2*udd;
khat=M/(dt^2)+(c/2*dt);
a=(M/(dt)^2)-c/(2*dt);
b=ks-(2*M/dt^2);

% initialize vectors
phat = []; 
u= [um1 uo]; 
for i=1:size(Ag)
    phat(i-1)=p(i+1)-a*um1(i-1)-b*u1;
    u(i+1) = phat(i+1)/khat; 
end

Answer 1

[VBBV]

u= [um1.' uo]; % transpose um1

[VBBV]

for i=2:size(Ag)-1

Matlab uses one based indexing for numeric arrays.

Answer 2

[Simon Chan]

Variable um1 is a column vector which have the same size as variable t or Ag. However, variable uo is a scalar which is equals to 0 in your case. Therefore, you get the mentioned error in

u= [um1 uo];

Furthermore, the indexing in the for-loop is also not correct since it is not possible to get phat(0) when i=1.

for i=1:size(Ag)
    phat(i-1)=p(i+1)-a*um1(i-1)-b*u1;
     u(i+1) = phat(i+1)/khat; 
end