< Code 1 >

x = [1:1:100 100:100:10000];

a = 1.0;

hFig = figure(1);

subplot(2,1,1);

y = a * log10(x);

plot(x,y,'b-','linewidth',2); grid on; xlabel('x'); ylabel('y');

ylim([0 6]);

subplot(2,1,2);

y = a * log10(x);

semilogx(x,y,'b-','linewidth',2); grid on; xlabel('x'); ylabel('y');

ylim([0 6]);

pos = [(i/50.0) 0.01 (1.0/50.0) 0.98];

set(hFig,'Position',[300 400 800 500])

< Code 2 >

x = [1:1:100 100:100:10000];

aList = [0.5 1.0 1.5];

hFig = figure(1);

subplot(2,1,1);

hold on;

for a = aList

   y = a * log10(x);

   plot(x,y,'b-','linewidth',2); grid on; xlabel('x'); ylabel('y');

end;

ylim([0 6]);

hold off;

subplot(2,1,2);

hold on;

for a = aList

   y = a * log10(x);

   semilogx(x,y,'b-','linewidth',2); grid on; xlabel('x'); ylabel('y');

end;

ylim([0 6]);

hold off;

%set(gca,'xtick',1:1:10);

pos = [(i/50.0) 0.01 (1.0/50.0) 0.98];

set(hFig,'Position',[300 400 800 500])