&DRIFT: MINIMISE


f_min

  The function to be minimised has to depend on at least one of
  the following variables:

  ------------------------------------------------------------------------
  Symbol         meaning
  ------------------------------------------------------------------------
  TIME           total drift time [micro seconds]
  LENGTH         length of the drift line [cm]
  DIFFUSION      integrated diffusion coefficient [cm]
  AVALANCHE      integrated and exponentiated Townsend coefficient
  LOSS           integrated and exponentiated attachment coefficient
  ------------------------------------------------------------------------

  The default function to be minimised is TIME.

SELECTION-FUNCTION

  This function should return either TRUE or FALSE. If FALSE is
  returned, then the point will not be considered anymore during
  the minimisation process.

  The following variables can be used:

  ------------------------------------------------------------------------
  Symbol         Meaning
  ------------------------------------------------------------------------
  TIME           total drift time [micro seconds]
  LENGTH         length of the drift line [cm]
  DIFFUSION      integrated diffusion coefficient [cm]
  AVALANCHE      integrated and exponentiated Townsend coefficient
  LOSS           integrated and exponentiated attachment coefficient
  STATUS         a string variable which can take the values:
                 "Left_Area", "Too_Many_Steps", "Abandoned",
                 "Hit_Plane", "Left_Drift_Medium", "Left_Mesh",
                 "Hit_X_Wire" and "Hit_X_Replica". "X" is the label that
                 you have assigned to the wire. Case is significant.
  ------------------------------------------------------------------------

  The default selection curve returns always TRUE.

ON

  ON should be followed be a parametrisation in terms of the
  variable T of the curve over which teh minimisation should
  take place.

  The range of T can be specified via RANGE.

  No default curve is provided.

RANGE

  RANGE should be followed by the minimum and the maximum value
  the variable T is allowed to take during minimisation, see
  ON for further information on T.

  No default RANGE is provided.

N

  The number of points on the curve for the initial scan of the
  curve.

  The default value for N is 20.

ELECTRON

  Requests that the minimisation be carried out for electrons.

  This is the default.

ION

  Requests that the minimisation be carried out for ions.

  By default, minimisation is done for electrons.

POSITIVE

  Requests that the minimisation be carried out for positively charged
  electrons or ions.

  The default is NEGATIVE.

NEGATIVE

  Requests that the minimisation be carried out for negatively charged
  electrons or ions.

  This is the default.

FUNCTION-PRECISION

  The procedure assumes it has converged if the relative change in
  function value has dropped below eps_f.

  The default value is 10E-4, which is also the smallest reasonable
  value on computers like Vax and IBM. On Cray and other computers
  with 64 bit precision, eps_f can be made smaller.

POSITIONAL-RESOLUTION

  The procedure assumes it has converged if the relative change in
  position of the minimum has dropped below eps_pos.

  The default value is 10E-4, which is also the smallest reasonable
  value on computers like Vax and IBM. On Cray and other computers
  with 64 bit precision, eps_pos can be made smaller.

ITERATE-LIMIT

  The maximum number of iteration steps during the minimisation
  process.

  By default 20.

PRINT

  Requests some printout during the minimisation procedure.

  This is default.

DATASET

  Requests dataset output of the minimisation results.

  No such output is produced by default.

Keyword index. Formatted on 10/11/98.