HP35S solver questions  extremum Message #1 Posted by x34 on 30 Jan 2011, 11:23 a.m.
HP35S Solver differs from the one of HP33S at least in two aspects:
a) It permits user to STOre the values in registers.
b) It is much prone not to find/show extremums of function solved.
(if HP33s while failed to find a root. usually makes it possible to see closest values, HP35S does not show them, i dunno why).
Regarding STOrage: if you store subexpression (like X>C*Y+3, where ">" designates "STO") or whole expression (X*Y+3>C), it's ok but of little use (sometimes you can get argument and/or function estimates after NO ROOT FND). But if you RCL it, solve would ask for it's value, effectively blocking usage of it for temporary data storage.
May be, the creators of HP35s wanted to make Solver more advanced (hence the ability to use STO in EQN), but had no resources to implement reasonable additional functionality.
Well, the EQN and STO are very interesting, and should be examined more closely. Especially, using indirect registers, there may be possibility to break into calc internals here (i hope so).
Interesting thing, that usage of X>X is allowed in the EQN. I do not understand the logic yet, however.
I am now trying to write some kind of equation permitting to use Solver for extremum search. The simplest way seems to compute derivative function and find it's roots.
