Introduction

    - How does Xi work? -

    Xi's main characteristic is it's interpretativ principle. The user simply types in a command and gets the result in seconds. Nevertheless self-defined subroutines or batch-operating is possible. Since Xi's statements are mostly based on C it's easy to get quick results for tolerably C-experienced users.

    For visualisation purposes Xi supports

    • 2D-plots
      • function plots
      • contour plots
      • velocity fields
      • image processing
      • mutli plots
    • 3D-plots
      • function plots
      • surfaces
      • velicity fields

    Output can be generated for X11, encapsulated PostScript, PPM and for the raytracer Povray. A highlight of the program is it's vector-oriented X11 graphic device which allows the user to freely change size and relativ position of the plots in a single window. Another feature is the unlimited redo/undo function. Xi supports the message passing system PVM to accelerate complex visualisations by using a workstation cluster as a parallel computer. Also included are standard and advanced techniques for image processing like fourier domain filtering or non linear filters etc.

    The Numerical library of Xi comes with a large number of algorithms and functions.

    • linear algebra
      • solving linear equations
      • inversion
      • QR-, LU-, SVD-decomposition
      • eigenvalues and eigenvectors
      • determinant
      • condition numbers
    • numerical integration and differentiation
    • interpolation, approximation and fits
      • cubic splines under tension
      • least-square-fits
      • least orthogonal distance fits
    • fast fourier transformation
    • multi-dim. ordinary differential equations
      • nonstiff methods (Adams)
      • stiff methods (BDF)
    • minimize sum of squares of nonlinear functions using levenberg-marquardt algorithm
    • finding zero of a system of nonlinear functions
    • special funtions
    • random number generators
    • complex funcions

    In contrast to common Fortan 77 or C-based numerical libraries you don't have to set all rather unimportant (and boring) parameters for complicated numerical algorithms because if wanted Xi does this job for you with (at least we hope) clever assumptions.


    Index © 1995 by Bodo Junglas, Klaus Spanderen and Fabian Weis
    - Last revised: April 23 1996