This is an implementation of quadratic fit for WP-34s. If only 3 points are entered, this may be used for quadratic interpolation.

Similar function was implemented in HP30b, if you missed it, here it is.

// (C) 2013 Andrew Nikitin

// Fit quadratic polynomial to empirical data// program operates in stack size 4

// uses regJ and regK to accumulate [SIGMA]x^3 and [SIGMA]x^4

// uses stat registers to accumulate other sums

// stores coefficients of quadrature fit in regA, regB, regC// Initialize:

// XEQ'QF'

// Clears sums, but not coefficients// Enter point:

// y ENTER x R/S (or [A])

// Result:

// number of points entered so far// Calculate coefficients (needs at least 3 points):

// [B]

// Result:

// a=regA=regZ

// b=regB=regY

// c=regC=regX

// (order compatible with SLVQ)// Evaluate Ax[^2]+Bx+C polynomial:

// x [C]

// Result:

// Ax[^2]+Bx+CLBL'QF'

SSIZE4

CL[SIGMA]

CLx

STO J

STO K

XEQ 00

STOP

XEQ A

BACK 002

// Accumulate sums, including [SIGMA]x^3 and [SIGMA]x^4

LBL A

[SIGMA]+

RCL L

ENTER

x^3

STO+ J

*

STO+ K

LBL 00

CLx

n[SIGMA]

RTN// delete point

LBL 65 // XEQ -

[SIGMA]-

RCL L

ENTER

x^3

STO- J

*

STO- K

GTO 00// Fit quadratic

LBL B

LocR 016

RCL K

STO .03

RCL J

STO .02

STO .06

# 002

n[SIGMA]

x<=? Y

ERR 15

STO .07

[SIGMA]x

STO .04

STO .08

[SIGMA]x[^2]

STO .01

STO .05

STO .09

[SIGMA]y

STO .12

[SIGMA]xy

STO .11

[SIGMA]x[^2]y

STO .10

1

1

3

.

0

3

0

3

ENTER

1

2

2

.

0

3

0

1

# 125

LINEQS

RCL .15

STO A

RCL .14

STO B

RCL .13

STO C

RTN// Evaluate Ax^2+Bx+C polynomial at regX

LBL C

ENTER

RCL* A

RCL+ B

*

RCL+ C

RTNEND