Implement function Riemann Zeta (#2975, #2950)

* Riemann Zeta Function

* Big Number zeta and added docs

* Original algorithm paper credited

* Update index.d.ts

* Update riemannZeta.js

* Update index.d.ts

* Renamed files to reflect zeta

* chore: make all the tests pass

* chore: refactor `zeta` (WIP)

* chore: reuse the validation logic of both number and BigNumber

* fix: type definitions of `zeta`

* fix: test the accuracy with numbers and BigNumbers (WIP)

* chore: make linter happy

* docs: fix example outputs

* docs: update history

* docs: update history

* docs: describe the limited precision of `zeta`

---------

Co-authored-by: BuildTools <anikpatel1322@gmail.com>
Co-authored-by: Anik Patel <74193405+Bobingstern@users.noreply.github.com>

HISTORY.md

@@ -2,6 +2,10 @@
 
 # unpublished changes since 11.9.1
 
+- Extend function `quantileSeq` with support for a `dimension` (#3002).
+  Thanks @dvd101x.
+- Implement #2735: Support indexing with an array of booleans (#2994),
+  for example `a[[true, false, true]]` and `a[a > 2]`. Thanks @dvd101x.
 - Fix #2990: `DenseMatrix` can mutate input arrays (#2991).
 
 

src/expression/embeddedDocs/embeddedDocs.js

@@ -184,6 +184,7 @@ import { setUnionDocs } from './function/set/setUnion.js'
 import { zpk2tfDocs } from './function/signal/zpk2tf.js'
 import { freqzDocs } from './function/signal/freqz.js'
 import { erfDocs } from './function/special/erf.js'
+import { zetaDocs } from './function/special/zeta.js'
 import { madDocs } from './function/statistics/mad.js'
 import { maxDocs } from './function/statistics/max.js'
 import { meanDocs } from './function/statistics/mean.js'
@@ -527,6 +528,7 @@ export const embeddedDocs = {
 
   // functions - special
   erf: erfDocs,
+  zeta: zetaDocs,
 
   // functions - statistics
   cumsum: cumSumDocs,

src/expression/embeddedDocs/function/special/zeta.js

@@ -0,0 +1,14 @@
+export const zetaDocs = {
+  name: 'zeta',
+  category: 'Special',
+  syntax: [
+    'zeta(s)'
+  ],
+  description: 'Compute the Riemann Zeta Function using an infinite series and Riemanns Functional Equation for the entire complex plane',
+  examples: [
+    'zeta(0.2)',
+    'zeta(-0.5)',
+    'zeta(4)'
+  ],
+  seealso: []
+}

src/factoriesAny.js

@@ -96,6 +96,7 @@ export { createFft } from './function/matrix/fft.js'
 export { createIfft } from './function/matrix/ifft.js'
 export { createSolveODE } from './function/numeric/solveODE.js'
 export { createErf } from './function/special/erf.js'
+export { createZeta } from './function/special/zeta.js'
 export { createMode } from './function/statistics/mode.js'
 export { createProd } from './function/statistics/prod.js'
 export { createFormat } from './function/string/format.js'

src/factoriesNumber.js

@@ -249,7 +249,7 @@ export { createUnequalNumber as createUnequal } from './function/relational/uneq
 
 // special
 export { createErf } from './function/special/erf.js'
-
+export { createZeta } from './function/special/zeta.js'
 // statistics
 export { createMode } from './function/statistics/mode.js'
 export { createProd } from './function/statistics/prod.js'

src/function/special/zeta.js

@@ -0,0 +1,140 @@
+import { factory } from '../../utils/factory.js'
+
+const name = 'zeta'
+const dependencies = ['typed', 'config', 'multiply', 'pow', 'divide', 'factorial', 'equal', 'smallerEq', 'isNegative', 'gamma', 'sin', 'subtract', 'add', '?Complex', '?BigNumber', 'pi']
+
+export const createZeta = /* #__PURE__ */ factory(name, dependencies, ({ typed, config, multiply, pow, divide, factorial, equal, smallerEq, isNegative, gamma, sin, subtract, add, Complex, BigNumber, pi }) => {
+  /**
+   * Compute the Riemann Zeta function of a value using an infinite series for
+   * all of the complex plane using Riemann's Functional equation.
+   *
+   * Based off the paper by Xavier Gourdon and Pascal Sebah
+   * ( http://numbers.computation.free.fr/Constants/Miscellaneous/zetaevaluations.pdf )
+   *
+   * Implementation and slight modification by Anik Patel
+   *
+   * Note: the implementation is accurate up to about 6 digits.
+   *
+   * Syntax:
+   *
+   *    math.zeta(n)
+   *
+   * Examples:
+   *
+   *    math.zeta(5)       // returns 1.0369277551433895
+   *    math.zeta(-0.5)    // returns -0.2078862249773449
+   *    math.zeta(math.i)  // returns 0.0033002236853253153 - 0.4181554491413212i
+   *
+   *
+   * @param {number | Complex | BigNumber} s   A Real, Complex or BigNumber parameter to the Riemann Zeta Function
+   * @return {number | Complex | BigNumber}    The Riemann Zeta of `s`
+   */
+  return typed(name, {
+    number: (s) => zetaNumeric(s, value => value, () => 20),
+    BigNumber: (s) => zetaNumeric(
+      s,
+      value => new BigNumber(value),
+      () => {
+        // epsilon is for example 1e-12. Extract the positive exponent 12 from that
+        return Math.abs(Math.log10(config.epsilon))
+      }
+    ),
+    Complex: zetaComplex
+  })
+
+  /**
+   * @param {number | BigNumber} s
+   * @param {(value: number) => number | BigNumber} createValue
+   * @param {(value: number | BigNumber | Complex) => number} determineDigits
+   * @returns {number | BigNumber}
+   */
+  function zetaNumeric (s, createValue, determineDigits) {
+    if (equal(s, 0)) {
+      return createValue(-0.5)
+    }
+    if (equal(s, 1)) {
+      return createValue(NaN)
+    }
+    if (!isFinite(s)) {
+      return isNegative(s) ? createValue(NaN) : createValue(1)
+    }
+
+    return zeta(s, createValue, determineDigits, s => s)
+  }
+
+  /**
+   * @param {Complex} s
+   * @returns {Complex}
+   */
+  function zetaComplex (s) {
+    if (s.re === 0 && s.im === 0) {
+      return new Complex(-0.5)
+    }
+    if (s.re === 1) {
+      return new Complex(NaN, NaN)
+    }
+    if (s.re === Infinity && s.im === 0) {
+      return new Complex(1)
+    }
+    if (s.im === Infinity || s.re === -Infinity) {
+      return new Complex(NaN, NaN)
+    }
+
+    return zeta(s, value => value, s => Math.round(1.3 * 15 + 0.9 * Math.abs(s.im)), s => s.re)
+  }
+
+  /**
+   * @param {number | BigNumber | Complex} s
+   * @param {(value: number) => number | BigNumber | Complex} createValue
+   * @param {(value: number | BigNumber | Complex) => number} determineDigits
+   * @param {(value: number | BigNumber | Complex) => number} getRe
+   * @returns {*|number}
+   */
+  function zeta (s, createValue, determineDigits, getRe) {
+    const n = determineDigits(s)
+    if (getRe(s) > -(n - 1) / 2) {
+      return f(s, createValue(n), createValue)
+    } else {
+      // Function Equation for reflection to x < 1
+      let c = multiply(pow(2, s), pow(createValue(pi), subtract(s, 1)))
+      c = multiply(c, (sin(multiply(divide(createValue(pi), 2), s))))
+      c = multiply(c, gamma(subtract(1, s)))
+      return multiply(c, zeta(subtract(1, s), createValue, determineDigits, getRe))
+    }
+  }
+
+  /**
+   * Calculate a portion of the sum
+   * @param {number | BigNumber} k   a positive integer
+   * @param {number | BigNumber} n   a positive integer
+   * @return {number}    the portion of the sum
+   **/
+  function d (k, n) {
+    let S = k
+    for (let j = k; smallerEq(j, n); j = add(j, 1)) {
+      const factor = divide(
+        multiply(factorial(add(n, subtract(j, 1))), pow(4, j)),
+        multiply(factorial(subtract(n, j)), factorial(multiply(2, j)))
+      )
+      S = add(S, factor)
+    }
+
+    return multiply(n, S)
+  }
+
+  /**
+   * Calculate the positive Riemann Zeta function
+   * @param {number} s   a real or complex number with s.re > 1
+   * @param {number} n   a positive integer
+   * @param {(number) => number | BigNumber | Complex} createValue
+   * @return {number}    Riemann Zeta of s
+   **/
+  function f (s, n, createValue) {
+    const c = divide(1, multiply(d(createValue(0), n), subtract(1, pow(2, subtract(1, s)))))
+    let S = createValue(0)
+    for (let k = createValue(1); smallerEq(k, n); k = add(k, 1)) {
+      S = add(S, divide(multiply((-1) ** (k - 1), d(k, n)), pow(k, s)))
+    }
+    return multiply(c, S)
+  }
+})

test/unit-tests/function/special/zeta.test.js

@@ -0,0 +1,94 @@
+/* eslint-disable no-loss-of-precision */
+
+import assert from 'assert'
+import approx from '../../../../tools/approx.js'
+import math from '../../../../src/defaultInstance.js'
+
+const zeta = math.zeta
+const epsilon = 1e-6 // FIXME: make zeta work with an epsilon of 1e-12
+
+function approxEqual (a, b) {
+  approx.equal(a, b, epsilon)
+}
+
+describe('Riemann Zeta', function () {
+  it('should calculate the Riemann Zeta Function of a positive integer', function () {
+    assert.ok(isNaN(zeta(1)))
+    approxEqual(zeta(2), 1.6449340668482264)
+    approxEqual(zeta(3), 1.2020569031595942)
+    approxEqual(zeta(4), 1.0823232337111381)
+    approxEqual(zeta(5), 1.0369277551433699)
+    assert.strictEqual(zeta(Infinity), 1) // shouldn't stall
+  })
+
+  it('should calculate the Riemann Zeta Function of a non-positive integer', function () {
+    assert.strictEqual(zeta(0), -0.5)
+    approxEqual(zeta(-1), -1 / 12)
+    approxEqual(zeta(-2), 0)
+    approxEqual(zeta(-3), 1 / 120)
+    approxEqual(zeta(-13), -1 / 12)
+    assert.ok(isNaN(zeta(-Infinity)))
+  })
+
+  it('should calculate the Riemann Zeta Function of a BigNumber', function () {
+    const bigEpsilon = 1e-5 // FIXME: should work with for example an epsilon of 1e-64
+    const digits = Math.abs(Math.log10(bigEpsilon))
+
+    const math2 = math.create()
+    math2.config({ epsilon: bigEpsilon })
+
+    function bigApproxEqual (a, b) {
+      assert.strictEqual(
+        a.toSignificantDigits(digits).valueOf(),
+        b.toSignificantDigits(digits).valueOf(),
+        (a + ' ~= ' + b + ' (epsilon: ' + epsilon + ')')
+      )
+    }
+
+    bigApproxEqual(zeta(math2.bignumber(0)), math2.bignumber('-0.5'))
+    assert.ok(zeta(math2.bignumber(1)).isNaN())
+    bigApproxEqual(zeta(math2.bignumber(2)), math2.bignumber('1.6449340668482264364724151666460251892189499012067984377355582293'))
+    bigApproxEqual(zeta(math2.bignumber(-2)).add(1), math2.bignumber('1')) // we add 1 on both sides since we cannot easily compare zero
+    bigApproxEqual(zeta(math2.bignumber(20)), math2.bignumber('1.0000009539620338727961131520386834493459437941874105957500564898'))
+    bigApproxEqual(zeta(math2.bignumber(-21)), math2.bignumber('-281.4601449275362318840579710144927536231884057971014492753623188'))
+    bigApproxEqual(zeta(math2.bignumber(50)), math2.bignumber('1.0000000000000008881784210930815903096091386391386325608871464644'))
+    bigApproxEqual(zeta(math2.bignumber(-211)), math2.bignumber('2.7274887879083469529027229775609299175103750961568681644229e231'))
+    bigApproxEqual(zeta(math2.bignumber(100)), math2.bignumber('1.0000000000000000000000000000007888609052210118073520537827660414'))
+    bigApproxEqual(zeta(math2.bignumber(Infinity)), math2.bignumber('1')) // shouldn't stall
+    bigApproxEqual(zeta(math2.bignumber(-Infinity)), math2.bignumber(NaN)) // shouldn't stall
+  })
+
+  it('should calculate the Riemann Zeta Function of a rational number', function () {
+    approxEqual(zeta(0.125), -0.6327756234986952552935)
+    approxEqual(zeta(0.25), -0.81327840526189165652144)
+    approxEqual(zeta(0.5), -1.460354508809586812889499)
+    approxEqual(zeta(1.5), 2.61237534868548834334856756)
+    approxEqual(zeta(2.5), 1.34148725725091717975676969)
+    approxEqual(zeta(3.5), 1.12673386731705664642781249)
+    approxEqual(zeta(30.5), 1.00000000065854731257004465)
+    approxEqual(zeta(144.9), 1.0000000000000000000000000)
+
+    approxEqual(zeta(-0.5), -0.2078862249773545660173067)
+    approxEqual(zeta(-1.5), -0.0254852018898330359495429)
+    approxEqual(zeta(-2.5), 0.00851692877785033054235856)
+  })
+
+  it('should calculate the Riemann Zeta Function of an irrational number', function () {
+    approxEqual(zeta(Math.SQRT2), 3.0207376794860326682709)
+    approxEqual(zeta(Math.PI), 1.17624173838258275887215)
+    approxEqual(zeta(Math.E), 1.26900960433571711576556)
+
+    approxEqual(zeta(-Math.SQRT2), -0.0325059805396893552173896)
+    approxEqual(zeta(-Math.PI), 0.00744304047846672771406904635)
+    approxEqual(zeta(-Math.E), 0.00915987755942023170457566822)
+  })
+
+  it('should calculate the Riemann Zeta Function of a Complex number', function () {
+    approxEqual(zeta(math.complex(0, 1)), math.complex(0.00330022368532410287421711, -0.418155449141321676689274239))
+    approxEqual(zeta(math.complex(3, 2)), math.complex(0.97304196041894244856408189, -0.1476955930004537946298999860))
+    approxEqual(zeta(math.complex(-1.5, 3.7)), math.complex(0.244513626137832304395, 0.2077842378226353306923615))
+    approxEqual(zeta(math.complex(3.9, -5.2)), math.complex(0.952389583517691366229, -0.03276345793831000384775143962))
+    approxEqual(zeta(math.complex(-1.2, -9.3)), math.complex(2.209608454242663005234, -0.67864225792147162441259999407))
+    approxEqual(zeta(math.complex(0.5, 14.14)), math.complex(-0.00064921838659084911, 0.004134963322496717323762898714))
+  })
+})

types/index.d.ts

@@ -2600,6 +2600,14 @@ declare namespace math {
      */
     erf<T extends number | MathCollection>(x: T): NoLiteralType<T>
 
+    /**
+     * Compute the Riemann Zeta function of a value using an infinite series
+     * and Riemann's Functional equation.
+     * @param s A real, complex or BigNumber
+     * @returns The Riemann Zeta of s
+     */
+    zeta<T extends number | Complex | BigNumber>(s: T): T
+
     /*************************************************************************
      * Statistics functions
      ************************************************************************/
@@ -5977,6 +5985,14 @@ declare namespace math {
       this: MathJsChain<T>
     ): MathJsChain<NoLiteralType<T>>
 
+    /**
+     * Compute the Riemann Zeta function of a value using an infinite series
+     * and Riemann's Functional equation.
+     */
+    zeta<T extends number | Complex | BigNumber>(
+      this: MathJsChain<T>
+    ): MathJsChain<T>
+
     /*************************************************************************
      * Statistics functions
      ************************************************************************/