MATLAB: Plot range with semilogx

Question

I am trying to use an array in my function, and then plot that same array as the x-axis. Even if I change "EfEm" to a single number (i.e. 400), it will not plot line. I believe my problem is wil "eta", but I am unsure on how to correct it so it will compute the range of EfEm. The correct output should be a line that starts flat, curves up from 10 to 200, and begins to plateau at around 400 until 1000.

% Constants and equations
EfEm = 0:1000;
xi = 2; 
eta = (EfEm - 1)/(EfEm + xi);
y70 = (1 + xi * eta * .7)/(1 - eta * .7);
% Plot
figure
semilogx(EfEm,y70, 'r');
ylim ([0,20]);
yticks([0,4,8,12,16,20]);
legend('V_f = 70%');
xlabel("E_f/E_m");
ylabel("E_2/E_m")
grid on

Answer 1

You needed element-wise instead of matrix division in these two lines:

eta = (EfEm - 1)./(EfEm + xi);
y70 = (1 + xi * eta * .7)./(1 - eta * .7);

Note where I used ./ instead of just / in the code. See the documentation on array vs. matrix operations.