left, right, bottom, top
Set the current world-coordinates of a plot.

PARAMETERS
----------
left    -    The world coordinate of the left edge of the current
             viewport.
right   -    The world coordinate of the right edge of the current
             viewport.
bottom  -    The world coordinate of the bottom edge of the current
             viewport.
top     -    The world coordinate of the top edge of the current
             viewport.

RELATED COMMANDS
----------------
pgsvp  -  Set the viewport for a new plot.
pgbox  -  Draw the world-coordinate axes of a plot.
pgenv  -  Set the viewport, the world coordinates and draw axes.
