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The documentation of the HP-71 Equation Solver (able to solve an equation for any variable) has been published a few days ago on literature.hpcalc.org.

This solver, written by C. Bunsen, has a special historical interest since it was an early prototype of the 18C/28C SOLVE interface, see the section "History and Inspiration of the Solve Interface" in the HP Journal, Aug. 1987, p. 10.

I knew the existence of this HP-71 solver from the HP Journal but never really tried to locate it until now.
As the documentation provides the names of the BASIC program and support files, it was now easy to find them in Joe Horn's collection.

To try it, just load the EQ, EQLEX and TPKEYS files from the LEXCOL.dat disc image file.
If you already have the ULIB52 LEX installed, then EQLEX is not needed (actually, it's better to use ULIB52 that fixes some bugs).
You also need the MATH ROM.

Thanks to Eric for scanning and sharing this up-to-now unreleased document, and thanks to the donor !

J-F

(edited: corrected the link - thanks Mark)

Your link was to the July 1987 issue rather than the August issue. Thanks for the Solver info, not to mention a great journal issue.

~Mark

Thanks J-F!!

I had found the files in the past, but w/o docs, were too complex to figure out.

I spoke with Eric last week when I saw this doc was coming, but had not noticed it had been scanned since then.

In my set of Joe's LEXes, the file containing these is "LEXCOL 71.lif" but my set may preceed the more widely distributed .zip file copy, where I think some filenames were simplified.

There is a video (somewhere...) of Chris saying the SOLVIT program for the 41 by Ted Beers was another predecessor/source of inspiration for his multi-variable solver, though the UI necessarily is a bit different and the equations are entered in FOCAL, not algebraic strings. I've just recently acquired a copy of this and will be posting it soon. Fortunately, since it was originally purchased from HP's User Library, it includes bar code, so program entry should be not so bad (the listing in the docs is in the TRACE mode with groups of instructions together on lines separated only where there are labels). Both of these have been long sought after in the community, so nice to be able to have them at last!

(11-24-2021 06:17 PM)rprosperi Wrote: [ -> ]There is a video (somewhere...) of Chris saying the SOLVIT program for the 41 by Ted Beers was another predecessor/source of inspiration for his multi-variable solver, though the UI necessarily is a bit different and the equations are entered in FOCAL, not algebraic strings. I've just recently acquired a copy of this and will be posting it soon.

In the cited section in the HP Journal, it is written:
"Paul Swadener implemented a version that would accomplish
this on several HP calculators. The variable was usually selected
by specifying a number corresponding to the occurrence of the
variable as it mapped to a register in an RPN program that
represented the equation"
I don't know these RPN versions, and actually know nothing about Paul Swadener, except he is mentioned in the article Acknowledgments as the "financial consultant" of the team.
Does anybody know more ?

J-F