Error: In assignment A(I) = B, the number of elements in B and I must be the same - matlab

Question

I'm stuck on K2 as it brought up this error:
In an assignment A(I) = B, the number of elements in B and
I must be the same.
I ran the debugger and I found out that J4 alone was a vector while other variables were all scalar.
How can I resolve this error to have the plot?
Here is the code that I ran.
h1 = 1*10^-6;
h2 = (10:10:1500)*10^-6;
a = 62.5*10^-6;
b = a+h1;
c = b+h2;
alpha_1 = 0.55*10^-6;
alpha_2 = 17.2*10^-6;
alpha_3 = 14.2*10^-6;
zeta = 6.3*10^-6;
P11 = 0.121;
P12 = 0.27;
neff = 1.456;
U1 = 0.17;
U2 = 0.32;
U3 = 0.31;
E1 = 0.74*10^11;
E2 = 1.08*10^11;
E3 = 1.96*10^11;
n = 1;
while(n<=150)
J1(n) = E2*(b^2-a^2)*(1-U1)-E1*a^2*(1-U2)-E1*b^2*(1+U2);
J2(n) = 2*E1*b^2;
J3(n) = E1*E2*(b^2-a^2)*(alpha_2 - alpha_1);
J4(n) = 2*E3*(c(n)^2-b^2)*a^2;
J5(n) = E2*(b^2-a^2)*(1-U3)*b^2+E2*(b^2-a^2)*(1+U3)*c(n)^2-E3*(c(n)^2-b^2)*(1+U2)*a^2-E3*(c(n)^2-b^2)*(1-U2)*b^2;
J6(n) = E2*E3*(c(n)^2 - b^2)*(b^2-a^2)*(alpha_2-alpha_3);
K1(n) = ((alpha_3-alpha_1)*E3*(c(n)^2-b^2)+(alpha_2-alpha_1)*E2*(b^2-a^2))/(E1*a^2+E2*(b^2-a^2)+E3*(c(n)^2-b^2));
K2(n) = (J2*J6-J3*J5)/(J2*J4-J1*J5);
Sr(n) = (neff^2/2)*(P11+P12)*(((1-U1)*K2/E1)-U1*K1);
Sz(n) = (1+P12)*(K1-(2*U2*K2/E1));
St(n) = alpha_1+zeta;
Km(n) = St+Sz+Sr;
n=n+1;
end
plot(h2,Km)

Answer 1

To recap what was already said in one answer, here's how I would modify the code:
h1 = 1e-6;
h2 = (10:10:1500)*1e-6;
a = 62.5*1e-6;
b = a+h1;
c = b+h2;
alpha_1 = 0.55*1e-6;
alpha_2 = 17.2*1e-6;
alpha_3 = 14.2*1e-6;
zeta = 6.3*1e-6;
P11 = 0.121;
P12 = 0.27;
neff = 1.456;
U1 = 0.17;
U2 = 0.32;
U3 = 0.31;
E1 = 0.74*1e11;
E2 = 1.08*1e11;
E3 = 1.96*1e11;
% pre-allocate variables
J1 = zeros(size(h2));
J2 = zeros(size(h2));
J3 = zeros(size(h2));
J4 = zeros(size(h2));
J5 = zeros(size(h2));
J6 = zeros(size(h2));
K1 = zeros(size(h2));
K2 = zeros(size(h2));
Sr = zeros(size(h2));
Sz = zeros(size(h2));
for n=1:length(h2)
J1(n) = E2*(b^2-a^2)*(1-U1)-E1*a^2*(1-U2)-E1*b^2*(1+U2);
J2(n) = 2*E1*b^2;
J3(n) = E1*E2*(b^2-a^2)*(alpha_2 - alpha_1);
J4(n) = 2*E3*(c(n)^2-b^2)*a^2;
J5(n) = E2*(b^2-a^2)*(1-U3)*b^2+E2*(b^2-a^2)*(1+U3)*c(n)^2-E3*(c(n)^2-b^2)*(1+U2)*a^2-E3*(c(n)^2-b^2)*(1-U2)*b^2;
J6(n) = E2*E3*(c(n)^2 - b^2)*(b^2-a^2)*(alpha_2-alpha_3);
K1(n) = ((alpha_3-alpha_1)*E3*(c(n)^2-b^2)+(alpha_2-alpha_1)*E2*(b^2-a^2))/(E1*a^2+E2*(b^2-a^2)+E3*(c(n)^2-b^2));
K2(n) = (J2(n)*J6(n)-J3(n)*J5(n))/(J2(n)*J4(n)-J1(n)*J5(n));
Sr(n) = (neff^2/2)*(P11+P12)*(((1-U1)*K2(n)/E1)-U1*K1(n));
Sz(n) = (1+P12)*(K1(n)-(2*U2*K2(n)/E1));
end
St = alpha_1+zeta;
Km = Sz+Sr+St;
plot(h2,Km)
Notes:
I have used a for loop to ensure the vector lengths are consistent with h2
I have pre-allocated the variables for speed
I have added various (n) to K1, K2, J1, J2, etc... in the equations to have only scalar operations
I have moved stuff out of the for loop that didn't need to be there
This gives the following plot (in Octave)

Answer 2

I ran your code and I found out that the dimensions of the vectors used to compute K2 are not compatible, e.g. each of J2 and J6 is a 1-row by 2-columns vector and you cannot multiply those. This also applies for the other multiplications. Depending on what you want to compute, you should transpose either one of them in each multiplication.
FYI: J.' is the transposed version of J in MATLAB.