      1 /*
      2     Copyright 2008-2025
      3         Matthias Ehmann,
      4         Michael Gerhaeuser,
      5         Carsten Miller,
      6         Alfred Wassermann
      7
      8     This file is part of JSXGraph.
      9
     10     JSXGraph is free software dual licensed under the GNU LGPL or MIT License.
     11
     12     You can redistribute it and/or modify it under the terms of the
     13
     14       * GNU Lesser General Public License as published by
     15         the Free Software Foundation, either version 3 of the License, or
     16         (at your option) any later version
     17       OR
     18       * MIT License: https://github.com/jsxgraph/jsxgraph/blob/master/LICENSE.MIT
     19
     20     JSXGraph is distributed in the hope that it will be useful,
     21     but WITHOUT ANY WARRANTY; without even the implied warranty of
     22     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     23     GNU Lesser General Public License for more details.
     24
     25     You should have received a copy of the GNU Lesser General Public License and
     26     the MIT License along with JSXGraph. If not, see <https://www.gnu.org/licenses/>
     27     and <https://opensource.org/licenses/MIT/>.
     28  */
     29
     30 /*global JXG: true, define: true*/
     31 /*jslint nomen: true, plusplus: true*/
     32
     33 import Mat from "./math.js";
     34
     35 /**
     36  * Functions for extrapolation of sequences. Used for finding limits of sequences which is used for curve plotting.
     37  * @name JXG.Math.Extrapolate
     38  * @exports Mat.Extrapolate as JXG.Math.Extrapolate
     39  * @namespace
     40  */
     41 Mat.Extrapolate = {
     42     upper: 15,
     43     infty: 1e4,
     44
     45     /**
     46      * Wynn's epsilon algorithm. Ported from the FORTRAN version in
     47      * Ernst Joachim Weniger, "Nonlinear sequence transformations for the acceleration of convergence
     48      * and the summation of divergent series", Computer Physics Reports Vol. 10, 189-371 (1989).
     49      *
     50      * @param {Number} s_n next value of sequence, i.e. n-th element of sequence
     51      * @param {Number} n index of s_n in the sequence
     52      * @param {Array} e One-dimensional array containing the extrapolation data. Has to be supplied by the calling routine.
     53      * @returns {Number} New estimate of the limit of the sequence.
     54      *
     55      * @memberof JXG.Math.Extrapolate
     56      */
     57     wynnEps: function (s_n, n, e) {
     58         var HUGE = 1e20,
     59             TINY = 1e-15,
     60             f0 = 1, // f0 may be changed to other values, see vanden Broeck, Schwartz (1979)
     61             f,
     62             j,
     63             aux1,
     64             aux2,
     65             diff,
     66             estlim;
     67
     68         e[n] = s_n;
     69         if (n === 0) {
     70             estlim = s_n;
     71         } else {
     72             aux2 = 0.0;
     73             for (j = n; j > 0; j--) {
     74                 aux1 = aux2;
     75                 aux2 = e[j - 1];
     76                 diff = e[j] - aux2;
     77                 if (Math.abs(diff) <= TINY) {
     78                     e[j - 1] = HUGE;
     79                 } else {
     80                     f = (n - j + 1) % 2 === 1 ? f0 : 1;
     81                     e[j - 1] = aux1 * f + 1 / diff;
     82                 }
     83             }
     84             estlim = e[n % 2];
     85         }
     86
     87         return estlim;
     88     },
     89
     90     // wynnRho: function(s_n, n, e) {
     91     //     var HUGE = 1.e+20,
     92     //         TINY = 1.e-15,
     93     //         j, f,
     94     //         aux1, aux2, diff, estlim;
     95
     96     //     e[n] = s_n;
     97     //     if (n === 0) {
     98     //         estlim = s_n;
     99     //     } else {
    100     //         aux2 = 0.0;
    101     //         for (j = n; j >= 1; j--) {
    102     //             aux1 = aux2;
    103     //             aux2 = e[j - 1];
    104     //             diff = e[j] - aux2;
    105     //             if (Math.abs(diff) <= TINY) {
    106     //                 e[j - 1] = HUGE;
    107     //             } else {
    108     //                 f = ((n - j + 1) % 2 === 1) ? n - j + 1  : 1;
    109     //                 e[j - 1] = aux1 + f / diff;
    110     //             }
    111     //         }
    112     //         estlim = e[n % 2];
    113     //     }
    114
    115     //     return estlim;
    116     // },
    117
    118     /**
    119      * Aitken transformation. Ported from the FORTRAN version in
    120      * Ernst Joachim Weniger, "Nonlinear sequence transformations for the acceleration of convergence
    121      * and the summation of divergent series", Computer Physics Reports Vol. 10, 189-371 (1989).
    122      *
    123      * @param {Number} s_n next value of sequence, i.e. n-th element of sequence
    124      * @param {Number} n index of s_n in the sequence
    125      * @param {Array} a One-dimensional array containing the extrapolation data. Has to be supplied by the calling routine.
    126      * @returns {Number} New estimate of the limit of the sequence.
    127      *
    128      * @memberof JXG.Math.Extrapolate
    129      */
    130     aitken: function (s_n, n, a) {
    131         var estlim,
    132             HUGE = 1e20,
    133             TINY = 1e-15,
    134             denom,
    135             v,
    136             lowmax,
    137             j,
    138             m;
    139
    140         a[n] = s_n;
    141         if (n < 2) {
    142             estlim = s_n;
    143         } else {
    144             lowmax = n / 2;
    145             for (j = 1; j <= lowmax; j++) {
    146                 m = n - 2 * j;
    147                 denom = a[m + 2] - 2 * a[m + 1] + a[m];
    148                 if (Math.abs(denom) < TINY) {
    149                     a[m] = HUGE;
    150                 } else {
    151                     v = a[m] - a[m + 1];
    152                     a[m] -= (v * v) / denom;
    153                 }
    154             }
    155             estlim = a[n % 2];
    156         }
    157         return estlim;
    158     },
    159
    160     /**
    161      * Iterated Brezinski transformation. Ported from the FORTRAN version in
    162      * Ernst Joachim Weniger, "Nonlinear sequence transformations for the acceleration of convergence
    163      * and the summation of divergent series", Computer Physics Reports Vol. 10, 189-371 (1989).
    164      *
    165      * @param {Number} s_n next value of sequence, i.e. n-th element of sequence
    166      * @param {Number} n index of s_n in the sequence
    167      * @param {Array} a One-dimensional array containing the extrapolation data. Has to be supplied by the calling routine.
    168      * @returns {Number} New estimate of the limit of the sequence.
    169      *
    170      * @memberof JXG.Math.Extrapolate
    171      */
    172     brezinski: function (s_n, n, a) {
    173         var estlim,
    174             HUGE = 1e20,
    175             TINY = 1e-15,
    176             denom,
    177             d0,
    178             d1,
    179             d2,
    180             lowmax,
    181             j,
    182             m;
    183
    184         a[n] = s_n;
    185         if (n < 3) {
    186             estlim = s_n;
    187         } else {
    188             lowmax = n / 3;
    189             m = n;
    190             for (j = 1; j <= lowmax; j++) {
    191                 m -= 3;
    192                 d0 = a[m + 1] - a[m];
    193                 d1 = a[m + 2] - a[m + 1];
    194                 d2 = a[m + 3] - a[m + 2];
    195                 denom = d2 * (d1 - d0) - d0 * (d2 - d1);
    196                 if (Math.abs(denom) < TINY) {
    197                     a[m] = HUGE;
    198                 } else {
    199                     a[m] = a[m + 1] - (d0 * d1 * (d2 - d1)) / denom;
    200                 }
    201             }
    202             estlim = a[n % 3];
    203         }
    204         return estlim;
    205     },
    206
    207     /**
    208      * Extrapolated iteration to approximate the value f(x_0).
    209      *
    210      * @param {Number} x0 Value for which the limit of f is to be determined. f(x0) may or may not exist.
    211      * @param {Number} h0 Initial (signed) distance from x0.
    212      * @param {Function} f Function for which the limit at x0 is to be determined
    213      * @param {String} method String to choose the method. Available values: "wynnEps", "aitken", "brezinski"
    214      * @param {Number} step_type Approximation method. step_type = 0 uses the sequence x0 + h0/n; step_type = 1 uses the sequence x0 + h0 * 2^(-n)
    215      *
    216      * @returns {Array} Array of length 3. Position 0: estimated value for f(x0), position 1: 'finite', 'infinite', or 'NaN'.
    217      * Position 2: value between 0 and 1 judging the reliability of the result (1: high, 0: not successful).
    218      *
    219      * @memberof JXG.Math.Extrapolate
    220      * @see JXG.Math.Extrapolate.limit
    221      * @see JXG.Math.Extrapolate.wynnEps
    222      * @see JXG.Math.Extrapolate.aitken
    223      * @see JXG.Math.Extrapolate.brezinski
    224      */
    225     iteration: function (x0, h0, f, method, step_type) {
    226         var n,
    227             v,
    228             w,
    229             estlim = NaN,
    230             diff,
    231             r = 0.5,
    232             E = [],
    233             result = "finite",
    234             h = h0;
    235
    236         step_type = step_type || 0;
    237
    238         for (n = 1; n <= this.upper; n++) {
    239             h = step_type === 0 ? h0 / (n + 1) : h * r;
    240             v = f(x0 + h, true);
    241
    242             w = this[method](v, n - 1, E);
    243             //console.log(n, x0 + h, v, w);
    244             if (isNaN(w)) {
    245                 result = "NaN";
    246                 break;
    247             }
    248             if (v !== 0 && w / v > this.infty) {
    249                 estlim = w;
    250                 result = "infinite";
    251                 break;
    252             }
    253             diff = w - estlim;
    254             if (Math.abs(diff) < 1e-7) {
    255                 break;
    256             }
    257             estlim = w;
    258         }
    259         return [estlim, result, 1 - (n - 1) / this.upper];
    260     },
    261
    262     /**
    263      * Levin transformation. See Numerical Recipes, ed. 3.
    264      * Not yet ready for use.
    265      *
    266      * @param {Number} s_n next value of sequence, i.e. n-th element of sequence
    267      * @param {Number} n index of s_n in the sequence
    268      * @param {Array} numer One-dimensional array containing the extrapolation data for the numerator. Has to be supplied by the calling routine.
    269      * @param {Array} denom One-dimensional array containing the extrapolation data for the denominator. Has to be supplied by the calling routine.
    270      *
    271      * @memberof JXG.Math.Extrapolate
    272      */
    273     levin: function (s_n, n, omega, beta, numer, denom) {
    274         var HUGE = 1e20,
    275             TINY = 1e-15,
    276             j,
    277             fact,
    278             ratio,
    279             term,
    280             estlim;
    281
    282         term = 1.0 / (beta + n);
    283         numer[n] = s_n / omega;
    284         denom[n] = 1 / omega;
    285         if (n > 0) {
    286             numer[n - 1] = numer[n] - numer[n - 1];
    287             denom[n - 1] = denom[n] - denom[n - 1];
    288             if (n > 1) {
    289                 ratio = (beta + n - 1) * term;
    290                 for (j = 2; j <= n; j++) {
    291                     fact = (beta + n - j) * Math.pow(ratio, j - 2) * term;
    292                     numer[n - j] = numer[n - j + 1] - fact * numer[n - j];
    293                     denom[n - j] = denom[n - j + 1] - fact * denom[n - j];
    294                     term *= ratio;
    295                 }
    296             }
    297         }
    298         if (Math.abs(denom[0]) < TINY) {
    299             estlim = HUGE;
    300         } else {
    301             estlim = numer[0] / denom[0];
    302         }
    303         return estlim;
    304     },
    305
    306     iteration_levin: function (x0, h0, f, step_type) {
    307         var n,
    308             v,
    309             w,
    310             estlim = NaN,
    311             v_prev,
    312             delta,
    313             diff,
    314             omega,
    315             beta = 1,
    316             r = 0.5,
    317             numer = [],
    318             denom = [],
    319             result = "finite",
    320             h = h0,
    321             transform = "u";
    322
    323         step_type = step_type || 0;
    324
    325         v_prev = f(x0 + h0, true);
    326         for (n = 1; n <= this.upper; n++) {
    327             h = step_type === 0 ? h0 / (n + 1) : h * r;
    328             v = f(x0 + h, true);
    329             delta = v - v_prev;
    330             if (Math.abs(delta) < 1) {
    331                 transform = "u";
    332             } else {
    333                 transform = "t";
    334             }
    335             if (transform === "u") {
    336                 omega = (beta + n) * delta; // u transformation
    337             } else {
    338                 omega = delta; // t transformation
    339             }
    340
    341             v_prev = v;
    342             w = this.levin(v, n - 1, omega, beta, numer, denom);
    343             diff = w - estlim;
    344             // console.log(n, delta, transform, x0 + h, v, w, diff);
    345
    346             if (isNaN(w)) {
    347                 result = "NaN";
    348                 break;
    349             }
    350             if (v !== 0 && w / v > this.infty) {
    351                 estlim = w;
    352                 result = "infinite";
    353                 break;
    354             }
    355             if (Math.abs(diff) < 1e-7) {
    356                 break;
    357             }
    358             estlim = w;
    359         }
    360         return [estlim, result, 1 - (n - 1) / this.upper];
    361     },
    362
    363     /**
    364      *
    365      * @param {Number} x0 Value for which the limit of f is to be determined. f(x0) may or may not exist.
    366      * @param {Number} h0 Initial (signed) distance from x0.
    367      * @param {Function} f Function for which the limit at x0 is to be determined
    368      *
    369      * @returns {Array} Array of length 3. Position 0: estimated value for f(x0), position 1: 'finite', 'infinite', or 'NaN'.
    370      * Position 2: value between 0 and 1 judging the reliability of the result (1: high, 0: not successful).
    371      * In case that the extrapolation fails, position 1 and 2 contain 'direct' and 0.
    372      *
    373      * @example
    374      * var f1 = (x) => Math.log(x),
    375      *     f2 = (x) => Math.tan(x - Math.PI * 0.5),
    376      *     f3 = (x) => 4 / x;
    377      *
    378      * var x0 = 0.0000001;
    379      * var h = 0.1;
    380      * for (let f of [f1, f2, f3]) {
    381      *     console.log("x0=", x0, f.toString());
    382      *     console.log(JXG.Math.Extrapolate.limit(x0, h, f));
    383      *  }
    384      *
    385      * </pre><div id="JXG5e8c6a7e-eeae-43fb-a669-26b5c9e40cab" class="jxgbox" style="width: 300px; height: 300px;"></div>
    386      * <script type="text/javascript">
    387      *     (function() {
    388      *         var board = JXG.JSXGraph.initBoard('JXG5e8c6a7e-eeae-43fb-a669-26b5c9e40cab',
    389      *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
    390      *     var f1 = (x) => Math.log(x),
    391      *         f2 = (x) => Math.tan(x - Math.PI * 0.5),
    392      *         f3 = (x) => 4 / x;
    393      *
    394      *     var x0 = 0.0000001;
    395      *     var h = 0.1;
    396      *     for (let f of [f1, f2, f3]) {
    397      *         console.log("x0=", x0, f.toString());
    398      *         console.log(JXG.Math.Extrapolate.limit(x0, h, f));
    399      *      }
    400      *
    401      *     })();
    402      *
    403      * </script><pre>
    404      *
    405      *
    406      * @see JXG.Math.Extrapolate.iteration
    407      * @memberof JXG.Math.Extrapolate
    408      */
    409     limit: function (x0, h0, f) {
    410         return this.iteration_levin(x0, h0, f, 0);
    411         //return this.iteration(x0, h0, f, 'wynnEps', 1);
    412
    413         // var algs = ['wynnEps', 'levin'], //, 'wynnEps', 'levin', 'aitken', 'brezinski'],
    414         //     le = algs.length,
    415         //     i, t, res;
    416         // for (i = 0; i < le; i++) {
    417         //     for (t = 0; t < 1; t++) {
    418         //         if (algs[i] === 'levin') {
    419         //             res = this.iteration_levin(x0, h0, f, t);
    420         //         } else {
    421         //             res = this.iteration(x0, h0, f, algs[i], t);
    422         //         }
    423         //         if (res[2] > 0.6) {
    424         //             return res;
    425         //         }
    426         //         console.log(algs[i], t, res)
    427         //     }
    428         // }
    429         // return [f(x0 + Math.sign(h0) * Math.sqrt(Mat.eps)), 'direct', 0];
    430     }
    431 };
    432
    433 export default Mat.Extrapolate;
    434