Tcl/Tk-based programs. IV. CALCRYS: crystallographic calculator

1. The crystallographic problem Crystallographers need to make a number of simple algebraic calculations in order to obtain lengths, angles, define relations between molecules, transformations of the coordinates, etc. These calculations can be performed by general means, e.g. either with a pocket calculator or with a computer using standard mathematical packages. Another possibility is to have a specialized tool, tuned particularly to these calculations, easy to call and to use, and fast to address the problem.