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31. Number Theory


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31.1 Functions and Variables for Number Theory

Function: bern (n)

Returns the n'th Bernoulli number for integer n. Bernoulli numbers equal to zero are suppressed if zerobern is false.

See also burn.

(%i1) zerobern: true$
(%i2) map (bern, [0, 1, 2, 3, 4, 5, 6, 7, 8]);
                  1  1       1      1        1
(%o2)       [1, - -, -, 0, - --, 0, --, 0, - --]
                  2  6       30     42       30
(%i3) zerobern: false$
(%i4) map (bern, [0, 1, 2, 3, 4, 5, 6, 7, 8]);
            1  1    1   5     691   7    3617  43867
(%o4) [1, - -, -, - --, --, - ----, -, - ----, -----]
            2  6    30  66    2730  6    510    798

Categories:  Number theory

Function: bernpoly (x, n)

Returns the n'th Bernoulli polynomial in the variable x.

Categories:  Number theory

Function: bfzeta (s, n)

Returns the Riemann zeta function for the argument s. The return value is a big float (bfloat); n is the number of digits in the return value.

load ("bffac") loads this function.

Function: bfhzeta (s, h, n)

Returns the Hurwitz zeta function for the arguments s and h. The return value is a big float (bfloat); n is the number of digits in the return value.

The Hurwitz zeta function is defined as

sum ((k+h)^-s, k, 0, inf)

load ("bffac") loads this function.

Function: binomial (x, y)

The binomial coefficient x!/(y! (x - y)!). If x and y are integers, then the numerical value of the binomial coefficient is computed. If y, or x - y, is an integer, the binomial coefficient is expressed as a polynomial.

Examples:

(%i1) binomial (11, 7);
(%o1)                          330
(%i2) 11! / 7! / (11 - 7)!;
(%o2)                          330
(%i3) binomial (x, 7);
        (x - 6) (x - 5) (x - 4) (x - 3) (x - 2) (x - 1) x
(%o3)   -------------------------------------------------
                              5040
(%i4) binomial (x + 7, x);
      (x + 1) (x + 2) (x + 3) (x + 4) (x + 5) (x + 6) (x + 7)
(%o4) -------------------------------------------------------
                               5040
(%i5) binomial (11, y);
(%o5)                    binomial(11, y)

Categories:  Number theory

Function: burn (n)

Returns the n'th Bernoulli number for integer n. burn may be more efficient than bern for large, isolated n (perhaps n greater than 105 or so), as bern computes all the Bernoulli numbers up to index n before returning.

burn exploits the observation that (rational) Bernoulli numbers can be approximated by (transcendental) zetas with tolerable efficiency.

load ("bffac") loads this function.

Categories:  Number theory

Function: cf (expr)

Converts expr into a continued fraction. expr is an expression comprising continued fractions and square roots of integers. Operands in the expression may be combined with arithmetic operators. Aside from continued fractions and square roots, factors in the expression must be integer or rational numbers. Maxima does not know about operations on continued fractions outside of cf.

cf evaluates its arguments after binding listarith to false. cf returns a continued fraction, represented as a list.

A continued fraction a + 1/(b + 1/(c + ...)) is represented by the list [a, b, c, ...]. The list elements a, b, c, ... must evaluate to integers. expr may also contain sqrt (n) where n is an integer. In this case cf will give as many terms of the continued fraction as the value of the variable cflength times the period.

A continued fraction can be evaluated to a number by evaluating the arithmetic representation returned by cfdisrep. See also cfexpand for another way to evaluate a continued fraction.

See also cfdisrep, cfexpand, and cflength.

Examples:

Categories:  Continued fractions

Function: cfdisrep (list)

Constructs and returns an ordinary arithmetic expression of the form a + 1/(b + 1/(c + ...)) from the list representation of a continued fraction [a, b, c, ...].

(%i1) cf ([1, 2, -3] + [1, -2, 1]);
(%o1)                     [1, 1, 1, 2]
(%i2) cfdisrep (%);
                                  1
(%o2)                     1 + ---------
                                    1
                              1 + -----
                                      1
                                  1 + -
                                      2

Categories:  Continued fractions

Function: cfexpand (x)

Returns a matrix of the numerators and denominators of the last (column 1) and next-to-last (column 2) convergents of the continued fraction x.

(%i1) cf (rat (ev (%pi, numer)));

`rat' replaced 3.141592653589793 by 103993/33102 =3.141592653011902
(%o1)                  [3, 7, 15, 1, 292]
(%i2) cfexpand (%); 
                         [ 103993  355 ]
(%o2)                    [             ]
                         [ 33102   113 ]
(%i3) %[1,1]/%[2,1], numer;
(%o3)                   3.141592653011902

Categories:  Continued fractions

Option variable: cflength

Default value: 1

cflength controls the number of terms of the continued fraction the function cf will give, as the value cflength times the period. Thus the default is to give one period.

(%i1) cflength: 1$
(%i2) cf ((1 + sqrt(5))/2);
(%o2)                    [1, 1, 1, 1, 2]
(%i3) cflength: 2$
(%i4) cf ((1 + sqrt(5))/2);
(%o4)               [1, 1, 1, 1, 1, 1, 1, 2]
(%i5) cflength: 3$
(%i6) cf ((1 + sqrt(5))/2);
(%o6)           [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2]

Categories:  Continued fractions

Function: divsum (n, k)
Function: divsum (n)

divsum (n, k) returns the sum of the divisors of n raised to the k'th power.

divsum (n) returns the sum of the divisors of n.

(%i1) divsum (12);
(%o1)                          28
(%i2) 1 + 2 + 3 + 4 + 6 + 12;
(%o2)                          28
(%i3) divsum (12, 2);
(%o3)                          210
(%i4) 1^2 + 2^2 + 3^2 + 4^2 + 6^2 + 12^2;
(%o4)                          210

Categories:  Number theory

Function: euler (n)

Returns the n'th Euler number for nonnegative integer n.

For the Euler-Mascheroni constant, see %gamma.

(%i1) map (euler, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
(%o1)    [1, 0, - 1, 0, 5, 0, - 61, 0, 1385, 0, - 50521]

Categories:  Number theory

Constant: %gamma

The Euler-Mascheroni constant, 0.5772156649015329 ....

Categories:  Constants

Function: factorial (x)

Represents the factorial function. Maxima treats factorial (x) the same as x!. See !.

Function: fib (n)

Returns the n'th Fibonacci number. fib(0) equal to 0 and fib(1) equal to 1, and fib (-n) equal to (-1)^(n + 1) * fib(n).

After calling fib, prevfib is equal to fib (x - 1), the Fibonacci number preceding the last one computed.

(%i1) map (fib, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
(%o1)         [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

Categories:  Number theory

Function: fibtophi (expr)

Expresses Fibonacci numbers in expr in terms of the constant %phi, which is (1 + sqrt(5))/2, approximately 1.61803399.

Examples:

(%i1) fibtophi (fib (n));
                           n             n
                       %phi  - (1 - %phi)
(%o1)                  -------------------
                           2 %phi - 1
(%i2) fib (n-1) + fib (n) - fib (n+1);
(%o2)          - fib(n + 1) + fib(n) + fib(n - 1)
(%i3) fibtophi (%);
            n + 1             n + 1       n             n
        %phi      - (1 - %phi)        %phi  - (1 - %phi)
(%o3) - --------------------------- + -------------------
                2 %phi - 1                2 %phi - 1
                                          n - 1             n - 1
                                      %phi      - (1 - %phi)
                                    + ---------------------------
                                              2 %phi - 1
(%i4) ratsimp (%);
(%o4)                           0

Categories:  Number theory

Function: ifactors (n)

For a positive integer n returns the factorization of n. If n=p1^e1..pk^nk is the decomposition of n into prime factors, ifactors returns [[p1, e1], ... , [pk, ek]].

Factorization methods used are trial divisions by primes up to 9973, Pollard's rho method and elliptic curve method.

(%i1) ifactors(51575319651600);
(%o1)     [[2, 4], [3, 2], [5, 2], [1583, 1], [9050207, 1]]
(%i2) apply("*", map(lambda([u], u[1]^u[2]), %));
(%o2)                        51575319651600

Categories:  Number theory

Function: inrt (x, n)

Returns the integer n'th root of the absolute value of x.

(%i1) l: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]$
(%i2) map (lambda ([a], inrt (10^a, 3)), l);
(%o2) [2, 4, 10, 21, 46, 100, 215, 464, 1000, 2154, 4641, 10000]

Categories:  Number theory

Function: inv_mod (n, m)

Computes the inverse of n modulo m. inv_mod (n,m) returns false, if n is a zero divisor modulo m.

(%i1) inv_mod(3, 41);
(%o1)                           14
(%i2) ratsimp(3^-1), modulus=41;
(%o2)                           14
(%i3) inv_mod(3, 42);
(%o3)                          false

Categories:  Number theory

Function: jacobi (p, q)

Returns the Jacobi symbol of p and q.

(%i1) l: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]$
(%i2) map (lambda ([a], jacobi (a, 9)), l);
(%o2)         [1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0]

Categories:  Number theory

Function: lcm (expr_1, ..., expr_n)

Returns the least common multiple of its arguments. The arguments may be general expressions as well as integers.

load ("functs") loads this function.

Categories:  Number theory

Function: minfactorial (expr)

Examines expr for occurrences of two factorials which differ by an integer. minfactorial then turns one into a polynomial times the other.

(%i1) n!/(n+2)!;
                               n!
(%o1)                       --------
                            (n + 2)!
(%i2) minfactorial (%);
                                1
(%o2)                    ---------------
                         (n + 1) (n + 2)

Categories:  Number theory

Function: next_prime (n)

Returns the smallest prime bigger than n.

(%i1) next_prime(27);
(%o1)                       29

Categories:  Number theory

Function: partfrac (expr, var)

Expands the expression expr in partial fractions with respect to the main variable var. partfrac does a complete partial fraction decomposition. The algorithm employed is based on the fact that the denominators of the partial fraction expansion (the factors of the original denominator) are relatively prime. The numerators can be written as linear combinations of denominators, and the expansion falls out.

(%i1) 1/(1+x)^2 - 2/(1+x) + 2/(2+x);
                      2       2        1
(%o1)               ----- - ----- + --------
                    x + 2   x + 1          2
                                    (x + 1)
(%i2) ratsimp (%);
                                 x
(%o2)                 - -------------------
                         3      2
                        x  + 4 x  + 5 x + 2
(%i3) partfrac (%, x);
                      2       2        1
(%o3)               ----- - ----- + --------
                    x + 2   x + 1          2
                                    (x + 1)

Function: power_mod (a, n, m)

Uses a modular algorithm to compute a^n mod m where a and n are integers and m is a positive integer. If n is negative, inv_mod is used to find the modular inverse.

(%i1) power_mod(3, 15, 5);
(%o1)                          2
(%i2) mod(3^15,5);
(%o2)                          2
(%i3) power_mod(2, -1, 5);
(%o3)                          3
(%i4) inv_mod(2,5);
(%o4)                          3

Categories:  Number theory

Function: primep (n)

Primality test. If primep (n) returns false, n is a composite number and if it returns true, n is a prime number with very high probability.

For n less than 341550071728321 a deterministic version of Miller-Rabin's test is used. If primep (n) returns true, then n is a prime number.

For n bigger than 34155071728321 primep uses primep_number_of_tests Miller-Rabin's pseudo-primality tests and one Lucas pseudo-primality test. The probability that n will pass one Miller-Rabin test is less than 1/4. Using the default value 25 for primep_number_of_tests, the probability of n beeing composite is much smaller that 10^-15.

Option variable: primep_number_of_tests

Default value: 25

Number of Miller-Rabin's tests used in primep.

Function: prev_prime (n)

Returns the greatest prime smaller than n.

(%i1) prev_prime(27);
(%o1)                       23

Categories:  Number theory

Function: qunit (n)

Returns the principal unit of the real quadratic number field sqrt (n) where n is an integer, i.e., the element whose norm is unity. This amounts to solving Pell's equation a^2 - n b^2 = 1.

(%i1) qunit (17);
(%o1)                     sqrt(17) + 4
(%i2) expand (% * (sqrt(17) - 4));
(%o2)                           1

Categories:  Number theory

Function: totient (n)

Returns the number of integers less than or equal to n which are relatively prime to n.

Categories:  Number theory

Option variable: zerobern

Default value: true

When zerobern is false, bern excludes the Bernoulli numbers which are equal to zero. See bern.

Categories:  Number theory

Function: zeta (n)

Returns the Riemann zeta function if x is a negative integer, 0, 1, or a positive even number, and returns a noun form zeta (n) for all other arguments, including rational noninteger, floating point, and complex arguments.

See also bfzeta and zeta%pi.

(%i1) map (zeta, [-4, -3, -2, -1, 0, 1, 2, 3, 4, 5]);
                                     2              4
           1        1     1       %pi            %pi
(%o1) [0, ---, 0, - --, - -, inf, ----, zeta(3), ----, zeta(5)]
          120       12    2        6              90

Categories:  Number theory

Option variable: zeta%pi

Default value: true

When zeta%pi is true, zeta returns an expression proportional to %pi^n for even integer n. Otherwise, zeta returns a noun form zeta (n) for even integer n.

(%i1) zeta%pi: true$
(%i2) zeta (4);
                                 4
                              %pi
(%o2)                         ----
                               90
(%i3) zeta%pi: false$
(%i4) zeta (4);
(%o4)                        zeta(4)

Categories:  Number theory


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