x = 1:.01:10;
y1 = sin(x);
y2 = cos(x);
p = plot(x,y1,x,y2)
Line width, specified as a positive value in points, where 1 point = 1/72 of an inch. If the line has markers, then the line width also affects the marker edges.
The line width cannot be thinner than the width of a pixel. If you set the line width to a value that is less than the width of a pixel on your system, the line displays as one pixel wide.