Add String to Matlab Plot Annotation

I am trying to add an annotation to a plot that uses a variable from the workspace. I have used the below code, but the only output I get is 'Pf Size:'

Can someone please assist with the syntax?

dim = [.2 .5 .3 .3];
str = ('Pf Size:' num2str(pfSize));
annotation('textbox',dim,'String',str,'FitBoxToText','on');

Answer 1

[Chunru]

pfSize = 2;
dim = [.2 .5 .3 .3];
str = ['Pf Size:' num2str(pfSize)];  % use [] instead of ()
plot(rand(10,1))
annotation('textbox',dim,'String',str,'FitBoxToText','on');