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SUBROUTINE PLTVPH (XUSE,YUSE, NX,NY, WX,WY)
C$ (Plot Viewport - Horizontal)
C$ It is often desirable for contour plots to maintain a unit
C$ aspect ratio. When the data grid is square, the viewport
C$ routine PLTSQ will guarantee this, but for rectangular
C$ grids, the computation is best relegated to a separate
C$ routine, for which purpose this routine is provided. A
C$ standard outer horizontal standard paper size page will be
C$ established, defining the device space extent, around which
C$ a frame will be drawn with the usual <PLOT79> identifying
C$ label along the bottom edge. A viewport with a unit aspect
C$ ratio will be centered on this page, and will itself be
C$ framed. The arguments are:
C$
C$ (NX,NY)........Number of X and Y data points in the array
C$ to be graphed.
C$ (XUSE,YUSE)....Maximum usable width and height of the
C$ viewport on the unit square. If these
C$ exceed the page device space limits, the
C$ latter will be used instead.
C$ (WX,WY)........World-coordinate window extents (returned)
C$ such that a unit aspect ratio is maintained.
C$ The larger of these will be exactly 1.0. If
C$ labelling or other plotting is later to be
C$ done inside the viewport, then a call to the
C$ window coordinate routine, SETWW, with
C$ arguments (ZERO,WX,ZERO,WY) can be issued.
C$
C$ If the input arguments are unusable (NX or NY less than 2,
C$ XUSE or YUSE not in the unit interval), then a standard
C$ square viewport will be established without flagging an
C$ error condition.
C$ (08-JUN-85)