&OPTIMISE: SET
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]
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.]
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.
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Variable Meaning Notes
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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
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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.
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).
The maximum number of iterations you allow the program to make.
[The default setting is 10.]
By default, some optimisation information is printed each cycle. This
may be switched of by specifying NOPRINT.
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.
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Variable Meaning Notes
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X or R x- or r-Coordinate -
Y or PHI y- or phi-Coordinate -
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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).
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:
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Variable Meaning Notes
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X or R x- or r-Coordinate -
Y or PHI y- or phi-Coordinate -
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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.