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loglog plot command not working,gives linear plot. I need help to make it work

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Frederick Anokye
Frederick Anokye on 4 May 2020
Answered: dpb on 4 May 2020
% plot of radius of critical nucleus against temperature
Lf = 10.9375e8;
Gma = 0.176;
Teq = 1235;
nstep = 125;
storage = zeros(nstep,2);
for i=1:nstep
r = -(2*Gma*Teq)/(Lf*-del_T);
storage(i,:) = [del_T, r];
del_T = del_T + 1;
history = zeros(nstep,2);
q = storage(:,2);
for j = 1:nstep
Del_G = (4*pi*((q(j)^2)*Gma) + ((4/3)*pi*(q(j))^3)*((Lf*-del_T)/Teq));
history(j,:) = [del_T, Del_G];
del_T = del_T + 1;
figure(1); clf;
loglog((storage(:,1)),(storage(:,2)),'r-', 'linewidth',2)
xlabel('Temperature (K)');
ylabel('Critical Radius (m)');
title('Plot of Critical Radius vs. Temperature Q2a');
string = ' r* = -2*Gma*Teq/Lf*-del_T;';
text (200, 2.2e-10,string)
figure(2); clf;
loglog((history(:,1)),(history(:,2)),'r-', 'linewidth',2)
xlabel('Temperature (K)');
ylabel('Activation Free Energy (J)');
title('Plot of Activation Free Energy vs. Temperature Q2b');
string = ' Del G = 4*pi*((q(j)^2)*Gma + (4/3)*pi*(q(j))^3)*((Lf*-del_T)/Teq)';
text (-1500, 2.7e-10,string);
x = history(:,1);
y = history(:,2);
figure(3 ); clf;
loglog(x, (y*0.15625),'r-', 'linewidth',2)
xlabel('Temperature (K)');
ylabel('Heterogenous Nucleation');
title('Plot of Heterogenous Nucleation vs. Temperature Q2c');
grid on

Accepted Answer

dpb on 4 May 2020
The plots are correct; you simply do not have enough dynamic range of the variables from minimum to maximum values that the logarithmic nature of the axes is easily apparent.
The log axis could be observed by setting for Figure 1
ylim([1E-10 1E-9])
Of course, the data then will look essentially like a line with a very shallow negative slope at about 3.4E-10, but you'll be able to see the axis tick marks are logarithmically distributed.

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