
TRACER (CCP4: Supported Program)NAMEtracer  Lattice TRAnsformation and CEll ReductionSYNOPSIStracer[Keyworded input] DESCRIPTIONThe reduced cell is the unit cell with the smallest volume whose axes are the three shortest noncoplanar 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 nonacute 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 INPUTAvailable 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 0.51.0 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.ENDTerminate input.Transformation commandsThe 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 Acentred; 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.EXAMPLETITLE tracer test DEL 0.1 ! allowed discrepancy CELL 10.51 15.15 6.54 90 151.7 90 ! cell parameters CCENTRED ! supplied cell is Ccentred REDUCED ! find reduced cell END AUTHORS. L. Lawton 