Impressive HP-25 Library

[Namir]

Hi All,

A few months ago I downloaded a pdf file that contains a library of HP-25 programs (which I believe was published in the PPC journal (???)), many of which were written by James Davidson and other PPC members. I must admit that I am very impressed with Davidson's work who was able to squeeze cool math programs in the 49 steps (and less!) of the HP-25 (and remember that calculator has no subroutine support). I am currently looking at Newton's method as implemented by Davidson. I had to use an Excel spreadsheet to document/trace program execution for one iteration, keeping track of what's in the stack and the four memory register used. All I can say is WOW! In the absence of subroutines (normally needed to make coding Newton's method easy), Davidson has shown fantastic programming skills in being able to execute the code for function f(x) twice per iteration. His manipulation of the memory register that stores the tolerance value (which he also uses as a logical flag) is nothing short of genius!!! My hats of for James!!

Davidson has also programs for solving differential equations and Simpson's method that use very clever programming tricks!!!

Another person who comes to mind who has mastered coding math functions in the HP-25 is the late Swiss professor Peter Henrici who taught at ETH in Zurich. Henrici wrote (for Wiley) a book about coding math programs for the HP-25, pushing the HP-25 to its limits! Later, Peter and his wife wrote a similar book for the HP-33E (which had line-oriented subroutines).

Programmers like Davidson and Henrici (to name a few) illustrate clever and frugal use of machine resources. The advent of the PC with it's ever increasing memory and disk resources has spoiled our programming practices.

Namir