HP 15c Scientific manual ´ b.0 001-42,21,.0 002 003 004 005, Bring x-value into X-register

Appendix D: A Detailed Look at _ 231

If Error 8 is displayed as a result of a search that is concentrated in a local ―flat‖ region of the function, the estimates in the X- and Y-registers will be relatively close together or extremely small. Execute _ again using for initial estimates the numbers from the X- and Y- registers (or perhaps two numbers somewhat further apart). If the magnitude of the function is neither a minimum nor constant, the algorithm will eventually expand its search and find a more significant result.

Example: Investigate the behavior of the function

f(x) = 3 + e− x /10 − 2ex2e− x

as evaluated in the following subroutine.

Keystrokes	Display
¥	000–	Program mode.

´b.0 001–42,21,.0

a	002–	43 16
“	003–	16	e−	x	.
	004–	12
'
®	005–	34	Bring x-value into X-register.
x	006–	43 11	x2e−			x	.
*	007–	20
'	008–	12
2	009–	2
*	010–	20	− 2e x 2 e −					x	.
“	011–	16
®	012–	34	Bring x-value into X-register.
a	013–	43 16
“	014–	16
1	015–	1
0	016–	0