COMP: a basic non-linear last squares curve fitting package. [Interactive program for PDP-11/34 or 11/70]
To find a mathematical model which describes (fits) data from a process which is fundamentally nonlinear, one usually uses nonlinear least-squares techniques on maxicomputers. These usually run in batch mode with the user supplying a model and initial ''guesstimates'' of its parameters. However, fitting the model to the data can be considered an art because computer algorithms either converge to true solutions, or converge to erroneous solutions, or fail to converge, depending on the quality of the guesstimates. It is slow and expensive to try enough runs to obtain a logical solution (unless one makes lucky initial guesses). An interactive BASIC procedure was developed which runs on either the PDP-11/34 under RT-11 or the PDP-11/70 under IAS. These programs help the investigator quickly fit the model to the data and statistically evaluate the differences between the two. The parameter estimates thus determined may then be used as guesstimates for the more precise maxicomputer codes. The key to the system is the re-enterant nature of the curve fitting routine (allowed only with a language such as INTERPRETED BASIC). The user supplies estimates of the parameters for the selected model (18 are currently available, and users can easily write their own). The computer tries a few iterative refinements (by using Taylor series expansion of partial derivatives to obtain linearization) of the estimates in an attempt to minimize the deviations between the values predicted by the model and the observed data. The user can observe as the program executes whether the result is a logical solution. If not, he may stop the process, enter new guesstimates, and examine those results, try again, or select a new model.
- Research Organization:
- Battelle Pacific Northwest Labs., Richland, WA (USA)
- DOE Contract Number:
- EY-76-C-06-1830
- OSTI ID:
- 6720176
- Report Number(s):
- BNWL-SA-6473; CONF-771144-6
- Resource Relation:
- Conference: DECUS meeting, San Diego, CA, USA, 28 Nov 1977; Other Information: Portions of document are illegible
- Country of Publication:
- United States
- Language:
- English
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COMPUTER CODES
C CODES
LEAST SQUARE FIT
MATHEMATICAL MODELS
BASIC
NONLINEAR PROBLEMS
PDP COMPUTERS
SERIES EXPANSION
COMPUTERS
MAXIMUM-LIKELIHOOD FIT
NUMERICAL SOLUTION
PROGRAMMING LANGUAGES
990200* - Mathematics & Computers