HP 50g Graphing, 48gII Graphing manual Pos, Potential, Powexpand, String Substring List Obj

POS

Type:	Command
Description:	Position Command: Returns the position of a substring within a string or the position of an
	object within a list.
	If there is no match for obj or substring, POS returns zero.
Access:	!°LCHARS POS		( °is the leftshift of the		Nkey).
	!°LIST ELEM POS		( °is the leftshift of the		Nkey).
	@& NPOS
Input/Output:
		Level 2/Argument 1	Level 1/Argument 2	Level 1/Item 1
		“string”	“substring”	→	n
		{ list }	obj	→	n
	CHR, NUM,
See also:		REPL, SIZE, SUB
POTENTIAL
Type:	Command
Description:	Find the potential field function describing a field whose vector gradient is input. This command
	is the opposite of DERIV. Given a vector V it attempts to return a function U such that grad U
	is equal to V; ∇U = V . For this to be possible, CURL(V) must be zero, otherwise the command
	reports a “Bad Argument Value” error. Stepbystep			mode is available with this command.
Access:	Catalog, …µ
Input:	Level 2/Argument 1: A vector V of expressions.
	Level 1/Argument 2: A vector of the names of the variables.
Output:	Level 1/Item 1: A function U of the variables that is the potential from which V is derived. An
	arbitrary constant can be added, the command does not do this.
Flags:	Exact mode must be set (flag –105 clear).
	Numeric mode must not be set (flag –3 clear).

Radians mode must be set (flag –17 set). Stepbystep mode can be set (flag –100 set).

Example: To confirm that this command is the opposite of DERIV, use the output of the example in DERIV, and show that the result is the same as the input given in the DERIV example. Find the function of the spatial variables x, y, and z whose gradient is:

(4xy+z)i + (2x2 + 6yz)j + (x+3y2)k

Command: POTENTIAL([4*X*Y+Z, 2*X^2+6*Y*Z, X+3*Y^2], [X,Y,Z])

EXPAND(ANS(1))

Result: 2*Y*X^2+Z*X+3*Z*Y^2

See also: DERIV, VPOTENTIAL

POWEXPAND

Type:	Function
Description:	Rewrites an expression raised to a power as a product. If followed by repeated execution of
	DISTRIB allows an expression to be expanded fully, step by step.
Access:	!Ú REWRITE L
Input:	An expression raised to a power.

3174 Full Command and Function Reference