|Model fitting by least squares|
The first level of computer use in science and engineering is modeling. Beginning from physical principles and design ideas, the computer mimics nature. After this, the worker looks at the result and thinks a while, then alters the modeling program and tries again. The next, deeper level of computer use is that the computer itself examines the results of modeling and reruns the modeling job. This deeper level is variously called ``fitting'' or ``estimation'' or ``inversion.'' We inspect the conjugate-direction method of fitting and write a subroutine for it that will be used in most of the examples in this monograph.