VECTOR_PLOT is an executable FORTRAN90 program, using double precision
arithmetic, which plots a 2D vector field at scattered points.
VECTOR_PLOT reads a file of (X,Y) locations, and a file of (U,V)
vector values, and draws a plot of the corresponding vector field (U(X,Y),
V(X,Y)), and of the normalized direction field.
VECTOR_PLOT requires the user to specify a “scale factor” for the size
of the vectors. A factor of 1.0 is normal, and corresponds to drawing the trail
of particles that have traveled for one time unit under the influence of the
given velocity. A factor of 0.5 or 2.0 might be used to shorten or lengthen the
VECTOR_PLOT requires the user to specify a “thinning factor” to
discard some of the data. A factor of 1 keeps all the data. A factor of 2 should
throw away about every other column and every other row of data (if the (X,Y)
coordinates fall on a regular grid.) Thinning the data is a crude but useful
tool, because most data files contain far too many vectors to plot.
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