This post describes how to mark subplots as , , and and give a common title for all subplots.

Consider the case where we want to mark subplot(2,2,1) as . The circle around the letter is produced using latex command textcircled{a}. MatLab understands it as a latex command due to the ‘interpreter’ -> ‘latex’. It is placed at the desired location using MatLab’s text() command. Finally in MatLab this is produced by
text(0,0.9,’‘, ‘Interpreter’, ‘latex’);

By default MatLab creates title for each individual plot using title(' ') command. This can be override by using the code from Line-23 to Line-27. Here is the brief description…
set(gcf,'NextPlot','add'); draw the next object to the current figure without clearing any graphics objects already present.

axes; by itself, creates the default full-window axis and returns a handle to it.

set(gca,'Visible','off'); turn off the visibility of current axis

h = title('Common title for all subplots','fontweight','b'); Print the title to current axis and create the handle for this title, but not visible.

set(h,'Visible','on'); Make the title of this axis alone visible

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x=linspace(0,1);
%%%%% subplot-1 %%%%%
subplot(2,2,1)
plot(x,x)
xlabel('input signal');
text(0,0.90,'$textcircled{bf a}$', 'Interpreter', 'latex'); 
%%%%% subplot-2 %%%%%
subplot(2,2,2);
plot(x,x.^2);
xlabel('input signal');
text(0,0.90,'$textcircled{bf b}$', 'Interpreter', 'latex');
%%%%% subplot-3 %%%%%
subplot(2,2,3)
plot(x,x.^3);
xlabel('input');
text(0,0.90,'$textcircled{bf c}$', 'Interpreter', 'latex');
%%%%% subplot-4 %%%%%
subplot(2,2,4);
plot(x,x.^4);
xlabel('input');
text(0,0.90,'$textcircled{bf d}$', 'Interpreter', 'latex');
% Create a common title for all the subplots
set(gcf,'NextPlot','add');
axes; 
set(gca,'Visible','off'); 
h = title('Common title for all subplots','fontweight','b');
set(h,'Visible','on');

suptitle() can also be used to create common title for all subplots instead Line 23-27 in the above code. But the above code gives more flexibility in setting title options.