Calculating e^x-1 on classic HPs
01-13-2016, 03:46 PM
Post: #10
 Gerson W. Barbosa Senior Member Posts: 1,182 Joined: Dec 2013
RE: Calculating e^x-1 on classic HPs
(01-12-2016 08:16 PM)Dieter Wrote:  The following version returns ex–1 while it saves the Y-register. It also does not use R^ which is missing on some of the classic calculators.

Code:
e^x ENTER ENTER LastX x<>y LN - x<>y x LastX 1 - + RTN

Very nice, thank you!

Just tested it on the HP-12C. I've tried an hyperbolic function approach on the HP-15C using the identity

$e^{x}-1=\frac{2}{\coth \frac{x}{2}-1}$

Code:
 001-42.21.11   f LBL A 002-          2     2 003-         10     /  004-42.22.25   f HYP TAN 005-         15    1/x 006-           1    1 007-         30     - 008-           2    2 009-         34     x<>y 010-         10     / 011-     43 32  g RTN

However this will require two additional steps to handle x=0. Also, for |x| > 3 the results start to lose accuracy as tanh(|x/2|) approaches 1.