First cell in array is empty

Why is my first cell array empty in my variable a_th?

I should be getting:

[.02*(10^-6);

22.5*(10^-6);

0]

Instead I am getting an empty cell [ ].

I am running this program on R2017a.

%% thermal expansion

% Givens
theta = [0,90];
theta = theta*(pi/180);
a1 = 0.02*(10^-6);
a2 = 22.5*(10^-6);
a12 = 0;
delT = -75;

% Transformation Matrix
for i = 1:length(theta)
    m = cos(theta(i));             %angle [rad]
    n = sin(theta(i));             %angle [rad]
    T{i} = [m^2, n^2, 2*m*n;
        n^2, m^2, -2*m*n;
        -m*n, m*n, (m^2)-(n^2)];
end

% Thermal expansion and Thermal strains for all angles of ply 
for i = length(theta)
a_th{i} = T{i}*[a1;a2;a12];
ex = a_th{i}(1)*delT;     %ax*deltaT
ey = a_th{i}(2)*delT;     %ay*deltaT
exy = a_th{i}(3)*delT;    %axy*deltaT
e_th{i} = [ex;ey;exy];
end

Answer 1

[Adam Danz]

oops! Typo...

should be

for i = 1:length(theta)
    %   ^^
end

Two more unrelated tips:

1. Always pre-allocate your loop variables (shown below)
2. numel() is safer than length()

a_th = cell(size(theta));    % PRE-ALLOCATE
e_th = cell(size(theta));    % PRE-ALLOCATE
for i = 1:numel(theta)        % USE NUMEL
    . . .
end