TRACER (CCP4: Supported Program)
- Lattice TRAnsformation and CEll Reduction
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.
Available keywords are:
A title, maximum of 70 characters.
<del> is the absolute value of the largest permissible difference
between any two of the six reduced cell scalar products. Defaults to
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.
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.
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
S. L. Lawton