VEL Procedure

The VEL procedure draws a velocity (flow) field with arrows following the field proportional in length to the field strength. Arrows are composed of a number of small segments that follow the streamlines.

This routine is written in the IDL language. Its source code can be found in the file vel.pro in the lib subdirectory of the IDL distribution.

Examples

; Create a vector of X values:
X = DIST(20)
; Create a vector of Y values:
Y = SIN(X)*100
; Plot the vector field:
VEL, X, Y

Syntax

VEL, U, V [, NVECS=value] [, XMAX= value{xsize/ysize}] [, LENGTH=value{longest/steps}] [, NSTEPS=value] [, TITLE=string]

Arguments

U

The X component at each point of the vector field. U must be a 2-D array.

V

The Y component at each point of the vector field. V must have the same dimensions as U.

Keywords

LENGTH

The length of each arrow line segment expressed as a fraction of the longest vector divided by the number of steps. The default is 0.1.

NSTEPS

The number of shoots or line segments for each arrow. The default is 10.

NVECS

The number of vectors (arrows) to draw. If this keyword is omitted, 200 vectors are drawn.

TITLE

A string containing the title for the plot.

XMAX

X axis size as a fraction of Y axis size. The default is 1.0. This argument is ignored when !P.MULTI is set.

Version History

Pre-4.0

Introduced