HP 50g Solve on object?

[Giuseppe Donnini]

I would rather rely on the good ol' HP-48 routines still present in the HP-50G, and use the ROOT command.

ROOT is the programmable form of HP Solve and takes the following arguments:

+---------------+---------------------+------------------------------------------+
| Stack level 3 |  'alg' / << prog >> | 1. An algebraic expression or a program  |
|               |                     |    acting as the current equation.  Note |
|               |                     |    that the variable EQ is *not* used by |
|               |                     |    ROOT.                                 |
|               |                     |                                          |
| Stack level 2 |  'global'           | 2. The name of the unknown.              |
|               |                     |                                          |
| Stack level 1 |  guess / {guesses}  | 3. A number or a list of 1, 2, or 3      |
|               |                     |    numbers acting as initial guess(es).  |
+---------------+---------------------+------------------------------------------+

Don't forget the third argument! In contrast to its interactive implementation, the programmable version of the root-finder requires you to supply an initial guess. (The HP Solve environment uses a default guess if you don't supply one, which is simply the current value of the unknown variable, if it already exists, or zero, if it doesn't [formal variable]).

Note that ROOT only displays a message if an error occurs (Bad Guess(es) or Constant?). As it is not meant to be used interactively, it does not provide intrepretative messages when a root (or extremum) is actually found (Zero, Sign Reversal, or Extremum), nor does it allow you to monitor the root-finding process as during an HP Solve session.

Applying this to your example, we get the following program:

\<<             @ Begin program
  \<< X 5 + \>> @ Current equation
  'X'           @ Unknown
  0             @ Initial guess
  ROOT          @ Call root-finder
\>>             @ End program

Executing the program puts -5 on stack level 1, just as you wanted.