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PLTFV

       SUBROUTINE  PLTFV (V1,VDX,VDY,V2, MX,MY, NX,NY, SCALE, PL2)
 C$    (Flow Vectors)
 C$    Plot a  flow vector  field in  the current  viewport.   The
 C$    arguments are:
 C$
 C$    (V1,V2)........Range of vector magnitudes.  Vectors will be
 C$                   scaled so that a vector of maximum length V2
 C$                   will be 1/max(NX,NY)  units long  on a  unit
 C$                   square window,  and vectors  of length  less
 C$                   than V1 will not be plotted.
 C$    (MX,MY)........Actual  declared dimensions  of VDX(*,*) and
 C$                   VDY(*,*).
 C$    (NX,NY)........Cross-sections of VDX(*,*)  and VDY(*,*)  in
 C$                   use.  For best results, NX and NY should not
 C$                   exceed about 20.
 C$    VDX(I,J).......Vector  X-components   relative   to   point
 C$                   (X(I),Y(J)).
 C$    VDY(*,*).......Vector  Y-components   relative   to   point
 C$                   (X(I),Y(J)).
 C$    SCALE..........SCALE(X) is  a  function which  is  used  to
 C$                   scale the length  of a  vector.  "ABS"  will
 C$                   give linear scaling,  while "SQRT",  "ATAN",
 C$                   and "TANH"  achieve a  compression which  is
 C$                   often useful  to avoid  small vectors  being
 C$                   reduced to bare points.
 C$    PL2............2-dimensional pen movement routine, perhaps
 C$                   PL2CA.
 C$
 C$    (VDX(I,J),VDY(I,J)) together define  a flow  vector at  the
 C$    point (X(I),Y(J))  on  a  regular  rectangular  grid.   The
 C$    vectors are plotted  with a dot  at the point  (X(I),Y(J)),
 C$    with the tail of the vector extending away from the dot.
 C$    (19-MAR-83)