Copyleft (C) 2003 Glen Kilpatrick

Distributed under GNU General Public License

This program is supplied without representation or warranty of any kind. The author and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

In this context, the word "regression" refers to the simplification of a set of ordered pairs (of coordinates, for a scatter plot, or of independent and dependent variables in the more general sense) to a "best fit" trend line, and "polynomial" to this line being a function in higher powers of the independent variable.

To amplify by example on the above, most HP calculators will do a linear regression of sets of X,Y points; here the resultant best fit is an equation with X to the first power, or mX+b. Those that will also do a "power" fit will yield a quadratic equation, or power of two, a*X^{2}+b*X+c; cubic (also known as "spline" for the use of a thin strip of wood that used to be bent to fit pins on a board, and by flexing, or better, *relaxing* to minimum energy would reveal adjacent sections of different cubic equations) regression will be a power of three for X, *etc.*

This program will yield a polynomial curve fit of arbitrary power. But this requires more discussion. It should be obvious that a linear regression requires a minimum of two points, a quadratic three, a cubic four, *etc.*

If that is the case, then why not always pick a power that is one less than the number of points. The curve generated will pass through every point in the set (note that I gloss over multivalued sets, a particular X must yield one and only one Y), and the fit will be "perfect". The problem with this is that inherent measurement noise will be magnified, the curve will gyrate wildly outside the points in the set, the "energy" will be nowhere near minimized, and nothing will have been made simple.

In the real world, one will know that, *e.g.* measurements of a velocity distribution as a function of time will have a quadratic "dimension", as S=1/2*a*T^{2}+v*T+S[0] is a quadratic (yes, this is circular reasoning, but it's also an illustration of why picking the proper dimension to the problem is important). A cubic regression may yield a cubic equation, but the model won't be a good fit for reality whatever the regression coefficient is. See Dimensional Analysis for more on this way of approaching real-world modeling.

This program is a HP-42S port of PREGR (Polynomial Regression) or "Polynomial Curve Fit By Dennis York", "Copyright (c) 1992 Hewlett-Packard Company", which is itself based upon an HP-28S program submitted to HP by Dr. Robert C. Wyckoff.

Please see HP's example (and attribution to Dr. Wyckoff).

01>LBL "PREGR" 02 REAL? 03 GTO 00 04 GTO 15 05>LBL 00 06 ENTER 07 ENTER 08 IP 09 - 10 X=0? 11 GTO 01 12 R↓ 13 GTO 15 14>LBL 01 15 R↓ 16 X≤0? 17 GTO 15 18 X⇔Y? 19 MAT? 20 GTO 02 21 X⇔Y 22 GTO 15 23>LBL 02 24 ENTER 25 DIM? 26 X⇔Y 27 R↓ 28 2 29 X=Y? 30 GTO 16 31 R↓ 32 R↓ 33 X⇔Y 34>LBL 15 35 "USAGE: [n*2] of" 36 ⊢" [x,y]\lf→ Y, na" 37 ⊢"t# order → x \.." 38 AVIEW 39 STOP 40 "Inputs are save" 41 ⊢"d in\lfvars ΣDAT" 42 ⊢" & ord \.." 43 AVIEW 44 STOP 45 "[1+ord*1] ANS^ " 46 ⊢"← coefs\lfSOLVER" 47 ⊢" HRNR: x, f(x)" 48 ⊢"\.." 49 AVIEW 50 STOP 51 "PREGR uses STac" 52 ⊢"k, and\lfnames t" 53 ⊢"temp vars 'p*'" 54 AVIEW 55 STOP 56 GTO 15 57>LBL 16 58 "Initialization\lf" 59 AVIEW 60 WRAP 61 REALRES 62 CLV "ΣDAT" 63 CLV "ord" 64 CLV "ANS^" 65 CLV "x" 66 CLV "f(x)" 67 R↓ 68 R↓ 69 STO "ΣDAT" 70 X⇔Y 71 STO "ord" 72 1 73 + 74 1 75 NEWMAT 76 STO "ANS^" 77 STO "pM1" 78 2 79 RCLx "ord" 80 1 81 + 82 1 83 NEWMAT 84 STO "pM2" 85 1 86 RCL+ "ord" 87 ENTER 88 NEWMAT 89 STO "pM3" 90 1E-3 91 RCL× "ord" 92 STO "pLC1" 93 2 94 × 95 1 96 + 97 STO "pLC2" 98 1 99 ENTER 100 COMPLEX 101 STO "pIJ→" 102 STO "pIJ←" 103 "Loop 1" 104>LBL 17 105 AVIEW 106 0 107>LBL 18 108 INDEX "ΣDAT" 109 RCL "pIJ→" 110 COMPLEX 111 STOIJ 112 R↓ 113 R↓ 114 RCLEL 115 J+ 116 RCL "pLC1" 117 IP 118 y^{x}119 RCLEL 120 J+ 121 × 122 + 123 RCLIJ 124 COMPLEX 125 STO "pIJ→" 126 R↓ 127 FC? 77 128 GTO 18 129 INDEX "pM1" 130 RCL "pIJ←" 131 COMPLEX 132 STOIJ 133 R↓ 134 R↓ 135 STOEL 136 J+ 137 RCLIJ 138 COMPLEX 139 STO "pIJ←" 140 ⊢"." 141 ISG "pLC1" 142 GTO 17 143 "Loop 2" 144 INDEX "pM2" 145 RCL "ΣDAT" 146 DIM? 147 R↓ 148 STOEL 149 J+ 150 RCLIJ 151 COMPLEX 152 STO "pIJ←" 153>LBL 19 154 AVIEW 155 1 156 ENTER 157 COMPLEX 158 STO "pIJ→" 159 0 160>LBL 20 161 INDEX "ΣDAT" 162 RCL "pIJ→" 163 COMPLEX 164 STOIJ 165 R↓ 166 R↓ 167 RCLEL 168 I+ 169 RCL "pLC2" 170 IP 171 y^{x}172 + 173 RCLIJ 174 COMPLEX 175 STO "pIJ→" 176 R↓ 177 FC? 76 178 GTO 20 179 INDEX "pM2" 180 RCL "pIJ←" 181 COMPLEX 182 STOIJ 183 R↓ 184 R↓ 185 STOEL 186 J+ 187 RCLIJ 188 COMPLEX 189 STO "pIJ←" 190 ⊢"." 191 ISG "pLC2" 192 GTO 19 193 "Loop 3" 194 RCL "pIJ←" 195 STO "pIJ→" 196>LBL 21 197 AVIEW 198 INDEX "pM2" 199 RCL "pIJ→" 200 COMPLEX 201 STOIJ 202 RCLEL 203 I+ 204 RCLIJ 205 COMPLEX 206 STO "pIJ→" 207 R↓ 208 INDEX "pM3" 209 RCL "pIJ←" 210 COMPLEX 211 STOIJ 212 R↓ 213 R↓ 214 STOEL 215 J+ 216 RCLIJ 217 COMPLEX 218 STO "pIJ←" 219 FC? 76 220 GTO 21 221 FS? 77 222 GTO 03 223 RCL "pIJ←" 224 STO "pIJ→" 225 ⊢"." 226 GTO 21 227>LBL 03 228 RCL "pM1" 229 RCL÷ "pM3" 230 STO "ANS^" 231 CPXRES 232 CLV "pM1" 233 CLV "pM2" 234 CLV "pM3" 235 CLV "pLC1" 236 CLV "pLC2" 237 CLV "pIJ→" 238 CLV "pIJ←" 239 CLV "x" 240 CLV "f(x)" 241 CLST 242 "Done! SOLVER pg" 243 ⊢"m HRNR\lfcompute" 244 ⊢"s x _vs_ f(x)" 245 AVIEW 246 STOP 247 GTO "PREGR" 248>LBL "HRNR" 249 MVAR "x" 250 MVAR "f(x)" 251 INDEX "ANS^" 252 I- 253 RCL "x" 254 ENTER 255 ENTER 256 ENTER 257 0 258>LBL 04 259 × 260 RCLEL 261 I- 262 + 263 FC? 76 264 GTO 04 265 RCL- "f(x)" 266 END

LaBeLs PREGR, HRNR, 00, 01, 02, 03, 04, 15, 16, 17, 18, 19, 20, & 21. Variables ΣDAT, ord, ANS^, pM1, pM2, pM3, pLC1, pLC2, pIJ→, pIJ←, x, & f(x).

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