Programs in Physics & Physical Chemistry
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|Manuscript Title: NULLIJN: a program to calculate zero curves of a function of two variables of which one may be complex.|
|Authors: P.C. de Jagher|
|Program title: NULLIJN|
|Catalogue identifier: ACYL_v1_0|
Distribution format: gz
|Journal reference: Comput. Phys. Commun. 15(1978)351|
|Programming language: Fortran, Compass.|
|Computer: CDC CYBER 73/173.|
|Operating system: NOS/BE 1.1.|
|Program overlaid: yes|
|RAM: 51K words|
|Word size: 60|
|Peripherals: graph plotter, disc.|
|Keywords: General purpose, Implicitly defined Function, Zero curve, Plasma dispersion, Potential problem.|
Nature of problem:
When an algorithm for a function f of two variables, for instance a dispersion function f(w,k) or a potential V(r,z) is known, the program calculates and plots the zero curves, thus giving a graphical representation of an implicitly defined function. One of the variables may be complex.
A quadratic extrapolation, followed by a regula falsi algorithm to find a zero is used to calculate a succession of zero-points along a curve. The starting point of a curve is found by detecting a change of sign of the function on the edge of the area G that is examined.
Curves that lie entirely inside G are not found. Starting points of curves where the imaginary part of the complex variable is large might be missed.
The running time depends on the kind of function that is investigated. The algorithm for the evaluation of the function is usually executed 2000 - 30000 times.
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