&FIELD: PLOT-FIELD


contour

  Produces a plot of the lines of equal function values. The contours
  are labeled with the function value if the LABEL option is on (which
  is by default the case).

  The function is computed on the part of the viewing plane that is
  located within the current AREA box.

  If you request AUTOMATIC scaling of the range, contours are drawn
  at round values of the function over a range that covers the function
  values in the current AREA. The number of contours is used to compute
  a first estimate of the distance between two contours. This distance
  is rounded downwards to the first 10-fold multiple of 1, 2 or 5. The
  number of contours actually drawn is therefore usually larger than
  the number you requested.

  [The default function is V and the contours range by default from the
  highest to the lowest potential present in the cell. By default, 20
  contours are plotted.]

graph

  The function is evaluated on the track or on the curve specified
  with the ON keyword.

  The geometric aspects of the track, if used, should be set by means
  of the TRACK command before calling PLOT. Other aspects of the track,
  such as the clustering model, are not used in the present context.

  A curve should be parametrised in terms of T which will run from 0
  to 1. All 3 coordinates of the curve should be specified. Note that
  ON expects only one argument, the parametrisation should therefore
  be enclosed in quotes, e.g. 'cos(pi*t),sin(pi*t),0' would be
  appropriate to describe a semi-circle in the z=0 plane.

  The SCALE option can be used to force a vertical scale in the
  plot, this can for instance be useful if you intend to overlay
  various graphs.

  If you select the PRINT option, then the values plotted in the
  graph will also be printed out. Output re-routing (> file) can
  be used to write the values to a file.

  The number of sampling points can be set with N, default is 200.

  [The default function is V.]

histogram

  The function is sampled at GRID by GRID points on the part of
  the current viewing plane that is located inside the AREA box.
  The function values are entered in an histogram.

  This kind of plot can be useful to estimate the field homogeneity,
  provided the range has been tuned properly.

  The automatic search for proper binning (AUTOMATIC) uses the
  first few entries to set the range. Since the grid is scanned
  in a regular sequence, these entries are not necessarily
  representative for the entire sample, in particular if the
  number of bins is small compared to the grid size. See CALL ->
  BOOK_HISTOGRAM -> options -> AUTOMATIC for details on the
  automatic binning procedure.

  [The default function is E. The number of bins is preset to 100 and
  the range is by default chosen automatically.]

surface

  The function is sampled at GRID by GRID points on the part of
  the current viewing plane that is located inside the AREA box.
  The function values are presented as a three dimensional plot.
  The plot is first rotated by phi degrees around the z-axis and
  then tilted by theta degrees from the z-axis.

  This plot is decorative but it is generally agreed upon that it is
  hard to extract any meaningful information from it ...

  [The default function is V. The default viewing angles are 30 and 60
  degrees.]

vector

  This plot shows the flow of a 3-vector sampled at GRID by GRID
  points on the part of the current viewing plane that is located
  inside the AREA box. The vectors are displayed like geometrical
  objects.

  The z-component is set to 0, if not explicitely specified. For
  other than (x,y) views, this may give incorrect impressions.

  If used for (Ex,Ey,Ez), which is the default, one can pick out the
  location of the zeroes of the field and hence figure out roughly
  what the acceptance of a wire is.

  It is advisable to have roughly equal ranges in view of the scaling
  that is performed on the vectors.

  [The default functions are EX, EY, EZ.]

functions

  All functions (f1, f2 ... f7) should be expressions in terms of the
  following quantities:

  ----------------------------------------------------------------------
  Name        Meaning
  ----------------------------------------------------------------------
  X or R      x- or r-Coordinate of a point
  Y or PHI    y- or phi-Coordinate of a point
  Z           z-Coordinate of a point
  EX or ER    x- or r-Component of the electric field at (x/r,y/phi,z)
  EY or EPHI  x- or phi-Component of the electric field at (x/r,y/phi,z)
  EZ          z-Component of the electric field at (x/r,y/phi,z)
  E           Norm of the electric field at (x/r,y/phi,z)
  BX          x-Component of the magnetic field at (x/r,y/phi,z)
  BY          y-Component of the magnetic field at (x/r,y/phi,z)
  BZ          z-Component of the magnetic field at (x/r,y/phi,z)
  B           Norm of the magnetic field at (x/r,y/phi,z)
  V           Electrostatic potential at (x/r,y/phi,z)
  ----------------------------------------------------------------------

  Note: The variables BX and BY should not be used with cells that have
        been described in polar coordinates.

Keyword index. Formatted on 10/11/98.