Fourdem: A demonstration program for fourier synthesis and other cristallographic concepts

The cristallographic problem: In the experience of the authors, students frequently face problems understanding the abstract concepts of Fourier transformation and reciprocal space. The use of computers allows the demonstration of those concepts using multimedia presentations and computer simulations (Proffen & Neder, 1996). The program FOURDEM demonstrates specifically the Fourier synthesis technique. A version of the program running only on Macintosh computers was published by Welberry & Owen (1992). Among the frequent responses to this paper were various requests for a version of the program to run on IBM-PC compatible computers. As a result, a Microsoft Windows and a DOS version of the program FOURDEM have been developed and are now made available in addition to the Macintosh version. Method of solution: The input data (h, k, |F| and the phase φ) can either be entered interactively or be read from a file. On the Macintosh platform, two different programs are used, whereas the DOS and Windows versions allow one to use both modes in the same program. Further details of the applications of the program are given in Welberry & Owen (1992). Software environment: The Macintosh and DOS version of the program is written in standard Fortran77 with additional assembler and/or toolbox routines for the graphical interface. The Windows version is written in Turbo C++. All versions of FOURDEM are distributed as executables. Hardware environment: The program has been successfully used on various Macintosh and PowerMac platforms as well as on different DOS computers. The Macintosh version requires at least an 8-bit grey scale and a 640 × 480 display. The DOS version uses a VESA graphics driver (one such driver is included in the distribution) and uses a resolution of 800 × 600 pixels and a depth of 256 colours. The DOS version of the program needs about 550 kbytes of free memory. The Windows version will run using Windows 3.1 as well as Windows 95. There are no special hardware requirements for this version, although graphical output benefits from a colour depth of at least 256 colours. Disk space required for installation is below 1.4 Mbytes for all versions. Program specification: The synthesis of 50 reflections takes about 2 to 7 min depending on the computer used and the number of display updates required. Documentation: The program distribution for both platforms contains the program(s), example input files and a short manual describing the program and the required input and gives hints for the installation. Availability: The program for both platforms is available via the World Wide Web at http://rschp2.anu.edu.au:8080/proffen/fourdem/fourdem.html. The program can be used free of charge and authors having difficulties accessing the Internet can obtain a copy from the authors by sending a 3.5 in floppy disk.