Label a plot as contour function does

I want to label a plot using a label located on the drawed line, just as the countour function does.

I found that I can transform my function plot to a matrix (source) that I can give as input to the contour function

cols = 1:500 ;

rows = 150 + 100*sin(cols/100) ;

M = zeros(300,500) ;

idx = sub2ind(size(M), floor(rows), cols) ;

M(idx) = 1 ;

contour(M,'LevelList',1,'ShowText','on') ;

This produce the following figure

But this plot is not visible in all the domain, has two labels (I would like just one) and the label has not a white background (the number 1 intersect the line). How can I obtain a label like the following?

Answer 1

[Voss]

Sounds like you want to use text:

x = 1:500 ;
y = 150 + 100*sin(x/100) ;

plot(x,y)
text(50*pi,250,'1', ...
    'BackgroundColor','w', ...
    'HorizontalAlignment','center')
ylim([0 300])

[Filippo Manoli]

Thank you, that's exactly what I needed! :)

[Voss]

You're welcome!