Request for suggestions: algebraic equations in Free42

[Nigel (UK)]

(07-11-2020 08:04 AM)Vincent Weber Wrote:  

(07-10-2020 06:04 PM)Thomas Okken Wrote:  It looks like fully emulating the 27S/17B/etc. expression functionality will require implementing direct solutions. It sounds like this is rather simplistic, using additions and subtractions to isolate the unknown on one side of the equals sign, and using exact inverses to get it to its bare form. Is that really all there is to it? Is this documented anywhere?

This is described in details in the 27S/19B Technical applications book.
This will happen only if the unknown appears formally only once in the equation. So you can force iterative solutions by writing something like X+0*X rather than just X. Yes direct solutions are basic and straightforward, since the Pionniers are RPL-based a bit of RPL symbolics were embedded in them, but not much.

The direct solution feature can be annoying. For example, it means that solving \((x-5)^2-9=0\) will always return \(x=8\) as the solution regardless of the starting guess for \(x\), because \(\sqrt{9}\) is always taken as \(+3\). A similar thing can happen with an equation involving trig functions. Although the direct solution feature can be disabled, it would be simpler not to bother with it at all. The speed advantage that direct solution provides is surely unimportant on modern hardware.

Nigel (UK)