TRACER (CCP4: Supported Program)

NAME

tracer - Lattice TRAnsformation and CEll Reduction

SYNOPSIS

DESCRIPTION

The reduced cell is the unit cell with the smallest volume whose axes are the three shortest non-coplanar translations in the lattice. TRACER converts the cell given to the reduced cell. Reduction to a triclinic lattice with c<a<b and angles alpha and beta non-acute allows for the identification of the Bravais lattice of highest symmetry which it represents; this is done by calculation of the 6 scalar products a.a, a.b ... and comparison with matrices set up within the program. There are only 43 independent cells to consider.

KEYWORDED INPUT

Available keywords are:

ACENTRED, BCENTRED, CALCULATE, CCENTRED, CELL, DEL, END, FCENTRED, MATRIX, RCELL, REDUCED, TITLE, UCENTRED.

TITLE <title>

A title, maximum of 70 characters.

DEL <del>

<del> is the absolute value of the largest permissible difference between any two of the six reduced cell scalar products. Defaults to 1.0.

The <del> value imposes an upper limit on the equivalence of the special relationships between the scalar products. Usually the higher the standard deviation of cell parameters, the higher the value of <del> that should be used. For lattice parameters with errors of 1 part in 1000, a value for <del> of 0.5-1.0 is advised; for proteins, use at least 1.0. It is sensible to try more than one value and examine the results.

CELL <a> <b> <c> [ <alpha> <beta> <gamma> ]

Cell parameters (angles default to 90 degrees).

RCELL <a> <b> <c> <alpha> <beta> <gamma>

Reciprocal cell parameters. Don't omit the angles.

END

Terminate input.

Transformation commands

The following commands specify transformations of one cell to another. They are applied in the order in which they are given. A sequence of transformations is terminated by a REDUCED or CALCULATE command. After this, new ones may be started. Each transformation has an optional <tag>, which is up to 25 characters of information about it read from the rest of the line.

MATRIX <element> ... [ <tag> ]

Transform this cell to a new cell using the 9 supplied matrix elements in the order (1,1), (2,1) ... (2,3), (3,3).

ACENTRED [ <tag> ]

The initial cell is A-centred; transform it to primitive cell.

BCENTRED [ <tag> ]

CCENTRED [ <tag> ]

UCENTRED [ <tag> ]

FCENTRED [ <tag> ]

These are analogous to ACENTRED.

REDUCED [ <tag> ]

Get reduced cell; identify and generate from it the unit cell of highest symmetry and its corresponding lattice parameters.

CALCULATE [ <tag> ]

Do not transform this cell. This option may be used to identify the transformed cell and calculate its inverse cell parameters.

EXAMPLE

TITLE tracer test
DEL 0.1 ! allowed discrepancy
CELL 10.51 15.15 6.54 90 151.7 90 ! cell parameters
CCENTRED ! supplied cell is C-centred
REDUCED ! find reduced cell
END

AUTHOR

S. L. Lawton