(Bug?) HP48 Equation Library

[Han]

Well, I eventually did find an actual bug (or perhaps limitation) of the HP48 MES. According to this patent:

https://www.google.com/patents/US5175700

the MES basically automates the process of substituting in known values, and finding an equation that has only one unknown, solving that equation, then repeating the process after updating its list of known/solved values.

The problem with this is that an inconsistent system shows up as having a solution. For example:

Code:

{ 'X+Y=10' 'X+Y=11' } STEQ 1 'X' STO MINIT MSOLVR

Proceed to solve for Y and the HP48 produces:

Searching...
Solving for Y...
Y:9
Zero

Except X=1 Y=9 is only a zero of the first equation. There is no check at all whether that solution is in fact a solution to the system. I only noticed this when I started working on a hybrid solver engine that mimics the Multiple Equation Solver (MES).

In the meantime, I'm still interested in the formulas for the silicon density of states equations in the immediately previous post.