|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. Then the worker looks at the result, thinks a while, alters the modeling program, and tries again. The next, deeper level of computer use is that the computer examines the results of modeling and reruns the modeling job. This deeper level is variously called ``fitting,'' ``estimation,'' or ``inversion.'' We inspect the conjugate-direction method of fitting and write a subroutine for it that is used in most of the examples in this book.