&OPTIMISE: SET


distance

  The value of the maximum deviation between the target and the field
  function at which you will allow the iteration to stop.

  [Initial default: 1, remembered from one SET command to the next]

eps

  A small number used to check relative changes in the improvement and
  also to compute the numerical derivatives needed for the covariance
  matrix. Hence, a larger value (say 1) should be chosen when you know
  you are far from the optimised value and a smaller value (say 1E-4)
  when your initial guess is quite good.

  Values smaller than 1E-4 are harmful on machines with a limited single
  precision accuracy, like Apollo, IBM and Vax, because the covariance
  matrix is effectively a set of second derivatives. On Cray one might
  consider moving to smaller values.

  [The initial default setting is 1E-4, the value is remembered from
  one SET command to the next.]

field_function

  A function of the coordinates, the electrostatic field and potential,
  and some drift related quantities that will be made to resemble the
  target function as closely as possible.

  ----------------------------------------------------------------------
  Variable     Meaning                          Notes
  ----------------------------------------------------------------------
  X or R       x- or r-Coordinate               -
  Y or PHI     y- or phi-Coordinate             -
  EX or ER     x- or r-component of E           -
  EY or EPHI   y- or phi-component of E         -
  E            norm of E                        -
  V            potential                        -
  AVALANCHE    integrated Townsend coefficient  Not compatible with WIRE
  DIFFUSION    integrated diffusion             Not compatible with WIRE
  TIME         drift time                       Not compatible with WIRE
  ----------------------------------------------------------------------

  When using drift related quantities (AVALANCHE, DIFFUSION and TIME),
  one should take care to define a proper drift area via the DRIFT-AREA
  command. These quantities can not be used when optimising on the wire
  surface (WIRE option).

  More variables can be added on demand.

GRID

  Specifies that the grid should be used to compare the target and field
  functions.

  The density of the grid is set with the GRID command, please ensure
  that the number of grid points is not excessive.

  Do not forget to set a proper DRIFT-AREA if you wish to optimise drift
  related quantities (AVALANCHE, DIFFUSION and TIME).

iterlim

  The maximum number of iterations you allow the program to make.
  [The default setting is 10.]

PRINT

  By default, some optimisation information is printed each cycle. This
  may be switched of by specifying NOPRINT.

target_function

  A function of the coordinates that the program will try to reproduce
  with the field function by playing with the potentials.

  The alternative, AVERAGE, implies the field function is evaluated
  with the initial potential settings and that the resulting number
  is the target function for all points.

  ----------------------------------------------------------------------
  Variable     Meaning                          Notes
  ----------------------------------------------------------------------
  X or R       x- or r-Coordinate               -
  Y or PHI     y- or phi-Coordinate             -
  ----------------------------------------------------------------------

TRACK

  Specifies that the track should be used to compare the target and field
  functions.

  The number of track points can be set with POINTS.

  Do not forget to set a proper DRIFT-AREA if you wish to optimise drift
  related quantities (AVALANCHE, DIFFUSION and TIME).

weight_function

  By default the minimisation procedure tries to make the field function
  approach the target function the best it can, working equally hard for
  all points. If some points matter more than others, you alter this by
  assigning the important points a larger weight.

  The default weight for all points is 1, a weight is allowed to be
  negative but may not be zero.

  The weight function may depend only on the coordinates:

  ----------------------------------------------------------------------
  Variable     Meaning                          Notes
  ----------------------------------------------------------------------
  X or R       x- or r-Coordinate               -
  Y or PHI     y- or phi-Coordinate             -
  ----------------------------------------------------------------------

WIRES

  Specifies that the surface of the wires with code S should be used to
  compare the target and field functions.

  The number of points near the surface of each wire can be set with the
  POINTS command.

  Drift related quantities (AVALANCHE, DIFFUSION and TIME) can not be
  used in conjunction with WIRES.

Keyword index. Formatted on 10/11/98.