&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]

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 10\<SUP\>-4\</SUP\>) when your initial guess is quite good.

Values smaller than 10\<SUP\>-4\</SUP\> 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 10\<SUP\>-4\</SUP\>, 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 \φ-Coordinate	-
`EX or ER`	x- or r-component of E	-
`EY or EPHI`	y- or \φ-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 surface of one or more WIRES.

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 \φ-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 \φ-Coordinate	-

WIRES

Specifies that the surface of the wires with label 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.

Go to the top level, to &OPTIMISE, to SET, to the topic index, to the table of contents, or to the full text.

Formatted on 21/01/18 at 16:55.