# Why is this matrix instantly forming in the middle of the for loop?

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Joseph Zvonek on 7 Oct 2019
Commented: Joseph Zvonek on 7 Oct 2019
pi_c = [2 3 5 10 20 30];
M_0 = 0.1:0.1:3;
for i = 1:length(M_0)
tau_r = 1+(gamma-1)*M_0(i)^2/2;
for j = 1:length(pi_c)
tau_c = pi_c(j)^((gamma-1)/gamma);
tau_t = 1-(tau_r/tau_lambda)*(tau_c-1);
S_2 = c_p*T_0*g_c*(tau_lambda-tau_r*tau_c)./(a_0*h_PR*...
(sqrt(2*tau_lambda*(tau_r*tau_c*tau_t-1)/...
((gamma-1)*tau_r*tau_c))-M_0));
S_2_vec(i,j) = S_2*10^6;
end
end
When I run the program I get this error:
Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.
Error in HW4 (line 120)
S_2_vec(i,j) = S_2*10^6;
When I step through the program, the first time it calculates S_2, it instantly forms a 1x30 matrix, rather than just calculating one value for that iteration.
Any help would be greatly appreciated.
All the variables are shown below, the only 1x30 matrix is M_0 #### 1 Comment

meghannmarie on 7 Oct 2019
One of the variables used to calculate S_2 must be a matrix (probably a 1x30 matrix). You even use the dot operator for the division leading me to believe one of these is a matrix.
This is hard to troubleshoot without some sample data for all those unknown variables.

meghannmarie on 7 Oct 2019
When you calculate S_2, M_0 is subtracted in last part of the equation making it a 1x30 matrix. Should you be subtracting M_0(i)?
S_2 = c_p* ...other stuff in calculation... - M_0(i)))

#### 1 Comment

Joseph Zvonek on 7 Oct 2019
That was it, completely missed that, thank you!