PLOT_FIELD Procedure
Standard Library procedure that plots a two-dimensional velocity field.
Usage
PLOT_FIELD, u, v
Input Parameters
u — A 2D array giving the field vector at each point along the x-axis.
v — A 2D array giving the field vector at each point along the y-axis.
Keywords
Aspect — The aspect ratio of the final plot; that is, the ratio of the length of x-axis to the length of the y-axis. (Default: 1)
Length — The length of the longest field vector, expressed as a fraction of the plotting area. (Default: 0.1)
N — The number of arrows to draw. (Default: 200)
Title — A string containing the title of the plot. The default title is “Velocity Field”.
YLabelCenter — Controls whether the top and bottom major tick labels on a Y axis will be positioned within the boundaries of the axis box or centered across from the corresponding major tick.
Discussion
PLOT_FIELD picks N points at random and traces a path from each point along the field. The length of the path is proportional to Length and the field vector magnitude at that point.
Example
; Create the arrays.
u = FLTARR(21, 21)
v = FLTARR(21, 21)
; After you type .RUN, the WAVE> prompt changes to a dash (-)
; to indicate that you may enter a complete program unit.
.RUN
; This FOR loop puts values into array. The last END exits you
; from programming mode, compiles and executes the procedure,
; and then returns you to the WAVE> prompt.
FOR j=0L, 20 DO BEGIN
FOR i=0L, 20 DO BEGIN
x = 0.05 * FLOAT(i)
z = 0.05 * FLOAT(j)
u(i, j) = -SIN(!Pi * x) * COS(!Pi * z)
v(i, j) = COS(!Pi * x) * SIN(!Pi * z)
ENDFOR
ENDFOR
END
; Display the velocity field with default values as shown in
; the Figure: Velocity Field with Default Values.
PLOT_FIELD, u, v, Title = 'Velocity Field'
WAIT, 1
; Display the velocity field using 400 arrows as shown in
; the Figure: Velocity Field with 400 Arrows.
PLOT_FIELD, u, v, N = 400, Title = 'Velocity Field'
WAIT, 1
; Display the velocity field with individual modifications as
; shown in the Figure: Modified Velocity Field.
PLOT_FIELD, u, v, Aspect = .7, Length = .4, $
N = 20, Title = 'Example of PLOT_FIELD'
