and lw is less than 1.49 I get a thin line and when it is 1.50 or higher I get a thick line (thicker than I want). My understanding is that lw is a scalar, but here it is as if it is getting rounded to the nearest integer. Somehow I am not able to fine tune thickness this way. Any suggestions? I am using Matlab 2008a.
There's inevitable granularity owing to the screen being finite number of pixels. For a default figure here, the resolution works out for the display area that height is 342 pixels or 3.56 inches or roughly 95 pixels/inch. A point (linewidth units) is 1/72" so there's roughly 72/95 --> 0.758 pixels/point so rounding will cause the finite jumps in renderable line widths. That's just limitation of hardware; higher resolution the monitor, the better, of course, but it's not continuously variable in representation even though the math computation is much more precise.
as far as I know the only available line widths are 0.5, 1.0, 2.0, 3.0, 4.0 etc...I suspect it's a floating point to accommodate the 0.5 width. In my experience though, there usually isn't a difference between 0.5 and 1.0.