A computer program for graphical and iterative fitting of low and high order transfer functions to biological data

Abstract

A program, written for a Digital Equipment Corporation LAB-11 minicomputer (PDP-11/20), is described which enables the user to fit frequency response functions (equivalent to transfer functions for linear systems) to data resulting from frequency domain analysis of biological signals. The program is interactive, and the user may utilize graphical or numerical curve fitting techniques to obtain a transfer function equation and display it (evaluated at prescribed points) on a two color, point-plot display against a background of the experimental data points. The numerical curve fit of the transfer function uses a non-linear least squares method. A simple and efficient method for the calculation of high order partial derivatives permits high order as well as low order transfer functions to be fit to the experimental points. The program also allows “known” or predetermined transfer function equations to be “forced” through the experimental points. Statistical comparisons are made in the program as to “goodness of fit” between transfer functions of different orders, forms and origin (i.e., “forced” vis-à-vis “fit”). The resident driver program and the overlayable segments are written in standard FORTRAN IV; only the Bode diagram plot routine is written in assembly language.