Understanding the HP 28S XPON function

[mbrethen]

I guess I don't quite understand the usefulness of the XPON function on the HP 28S for symbolic expressions. I tried to evaluate the expression XPON("X^3") using ->NUM but it returns the error: Undefined Name. How does one, for example, determine the degree of a polynomial expression?

[Joe Horn]

XPON is only for real numbers, not algebraic objects. HP 28S RPL does not contain a command that returns the degree of a polynomial. The DEGREE command which does that was introduced into RPL later, in the HP 48G.

[Werner]

Probably the 50G, Joe. The 49G AUG does not know DEGREE.
(I have only a 48 and a 49, and I never heard of it - but that's not a reliable reference ;-)

Cheers, Werner

[mbrethen]

I wonder if this can be successfully programmed for the 28s? One thought I had is to perform successive differentiation until you end up with a constant? A loop counter could keep track of the number.

Another idea is to evaluate the polynomial using Horner's method (PVAL in the Math Applications reference) and then SIZE the nested list.

[Joe Horn]

(02-25-2017 12:43 PM)Werner Wrote:  Probably the 50G, Joe. The 49G AUG does not know DEGREE.
(I have only a 48 and a 49, and I never heard of it - but that's not a reliable reference ;-)

The 49G with firmware version 1.19-6 contains a DEGREE function that returns the degree of a polynomial. It's listed in the 49G's built-in CATALOG, and it has a help screen.

The 49G AUG is unfortunately missing an astounding number of 49G commands (at least they are missing from its Command Index on pages 427-432), including the following:

• ALGB
• ASSUME
• AUGMENT
• BASIS
• C2P
• CASCMD
• CHOLESKY
• CIRC
• COLLECT
• CONSTANTS
• CYCLOTOMIC
• DEF
• DEGREE
• DIAGMAP
• DISPXY
• DISTRIB
• DOMAIN
• DROITE
• EXP&LN
• EXP2HYP
• EXP2POW
• EXPLN
• FDISTRIB
• GAMMA
• GBASIS
• GRAMSCHMIDT
• GREDUCE
• HELP
• HYPERBOLIC
• IBASIS
• IMAGE
• INTEGER
• ISOM
• KER
• LASTARG
• LOCAL
• MAIN
• MATHS
• MKISOM
• MODULAR
• MSLV
• OLDPRT
• P2C
• PLOT
• PMINI
• POLYNOMIAL
• POP
• POTENTIAL
• POWEXPAND
• PUSH
• RCLVX
• REWRITE
• RULES
• SERIAL
• SIMPLIFY
• SREV
• STORE
• STOVX
• STURM
• STURMAB
• SYST2MAT
• TAN2CS2
• TESTS
• UNASSIGN
• UNASSUME
• UNBIND
• VPOTENTIAL

--- the commands in Library 256 are not included in the list above, but they were not in the 49G AUG either.

[Werner]

I stand corrected ;-)
At least it's the 49, not the 48 ;-)

Werner