Threaded Mode | Linear Mode

Dave Britten · 05-21-2015, 12:51 PM

I knocked out a simple lazy Newton's method solver (lazy in that it approximates the 1st derivative using f(1.000001x) and f(.999999x)), and it seems functional but definitely suboptimal. Here's the code for it, if you want to have a chuckle at my background obviously not being in numeric methods.

Code:

LBL "FN="

"FN="

AON

PROMPT

ASTO 20

AOFF

RTN

LBL "SOLVE"

"REG="

AOFF

PROMPT

STO 21

LBL "PSOLVE"

RCL IND 21

STO 22

LBL 00

CLA

ARCL X

AVIEW

STO IND 21

XEQ IND 20

STO 23

X=0?

GTO 04

RCL 22

1

1 E-6

-

*

STO IND 21

XEQ IND 20

STO 24

RCL 22

1

1 E-6

+

*

STO IND 21

XEQ IND 20

STO 25

RCL 24

-

X=0?

GTO 09

RCL 22

2 E-6

*

X<>Y

/

RCL 23

*

CHS

RCL 22

+

STO 22

GTO 00

LBL 04

RCL 22

RTN

LBL 09

RCL 23

RCL 22

RTN

END

LBL 09 is where it would check for extrema or discontinuities if I had implemented that part yet. I fed it numbers similar to my mortgage loan, and it obtained i%, but it wasn't exactly fast. Evaluating the function three times for every iteration really takes its toll on speed.

I'll have to study the HP-80 article more so as to have a better approximation of its algorithm. There's also a 19C/29C i% solver that uses Newton's method that's on the museum DVD (part of the general application book, I think), and I might be able to use some of that. I don't even necessarily need a general purpose solver, just one that's suited for handling the TVM equation.