MATLAB: The lines of graph doesn’t appear at matlab

k1 = 25;
k2 = 60;
nb = logspace(14,19);
n = length(nb);
for i = 1:n
vbr1(i) = k1*(nb(i)/1.0e16)^(-0.75); % Ge breakdown voltage
vbr2(i) = k2*(nb(i)/1.0e16)^(-0.75); % Si breakdown voltage
end
semilogx(nb,vbr1,'w', nb,vbr2,'w')
xlabel('Impurity Concentration, cm-3')
ylabel('Breakdown Voltage,V')
title('Breakdown Voltage vs. Impurity Concentration')
axis([1.0e14,1.0e17,0,2000])
text(2.0e14,270,'Ge')
text(3.0e14,1000,'Si')

Best Answer

You draw the lines in 'w': White line on white background. Try this:
semilogx(nb,vbr1,'r', nb,vbr2,'b')
Note: You do not need a loop to create the data:
nb   = logspace(14,19);
vbr1 = k1 * (nb / 1.0e16) .^ -0.75; % Ge breakdown voltage
vbr2 = k2 * (nb / 1.0e16) .^ -0.75; % Si breakdown voltage
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