Re: [Matplotlib-users] pcolor plot question about empty horizontal strip at top

[John H. <jdh...@ac...>]

>>>>> "seberino" == seberino  <seb...@sp...> writes:

    seberino> It seems if your grid has 20 rows ( different y values)
    seberino> of points that you won't get 20 colored horizontal
    seberino> strips but rather *19*.  This is because we must lose
    seberino> one row to specify the top and/or bottom EDGE of the
    seberino> plot.... so XX rows means (XX-1) rows of colored
    seberino> squares.

yep that's right, a frequent source of confusion.  

    seberino> Please tell me if this is right but more importantly,
    seberino> how to most wisely remove the white horizontal strip
    seberino> from this pcolor plot.

Well it would help if you posted your code, but my guess is that you
need to set your axis limits to equal your ymin/ymax of the pcolor.

Perhaps this example will give you a hint

   >>> pcolor(rand(10,7))  # no white strip...
   >>> ylim(0,11)          # a white strip because the ylim is wrong

In essence, the axis autoscaler will round up, eg 4990 to 5000, to
make nice integer ticks.  With pcolors and images, you often don't
want this, so use the axis, xlim, and/or ylim commands to set the
limits properly.

Eg

  ymin = min(ravel(Y))
  ymax = max(ravel(Y))
  ylim(ymin, ymax)

Also, if your x and y grids are equally spaced, you'll get much better
performance for large arrays, as well as more interpolation options,
if you use imshow with the extent kwarg to set the extent of your
image data.

JDH