det

NAME
    det - determinant

SYNOPSIS
    det(m)

TYPES
    m           square matrix with elements of suitable type

    return      zero or value of type determined by types of elements

DESCRIPTION
    The matrix m has to be square, i.e. of dimension 2 with:

        matmax(m,1) - matmin(m,1) == matmax(m,2) - matmin(m,2).

    If the elements of m are numbers (real or complex), det(m)
    returns the value of the determinant of m.

    If some or all of the elements of m are not numbers, the algorithm
    used to evaluate det(m) assumes the definitions of *, unary -, binary -,
    being zero or nonzero, are consistent with commutative ring structure,
    and if the m is larger than 2 x 2, division by nonzero elements is
    consistent with integral-domain structure.

    If m is a 2 x 2 matrix with elements a, b, c, d, where a tests as
    nonzero, det(m) is evaluated by

        det(m) = (a * d) - (c * b).

    If a tests as zero, det(m) = - ((c * b) - (a * d)) is used.

    If m is 3 * 3 with elements a, b, c, d, e, f, g, h, i, where a and
    a * e - d * b test as nonzero, det(m) is evaluated by

        det(m) = ((a * e - d * b) * (a * i - g * c)
                        - (a * h - g * b) * (a * f - d * c))/a.

EXAMPLE
    ; mat A[3,3] = {2, 3, 5, 7, 11, 13, 17, 19, 23}
    ; c = config("mode", "frac")
    ; print det(A), det(A^2), det(A^3), det(A^-1)
    -78 6084 -474552 -1/78

    ; obj res {r}
    ; global md
    ; define res_test(a) = !ismult(a.r, md)
    ; define res_sub(a,b) {local obj res v = {(a.r - b.r) % md}; return v;}
    ; define res_mul(a,b) {local obj res v = {(a.r * b.r) % md}; return v;}
    ; define res_neg(a) {local obj res v = {(-a.r) % md}; return v;}
    ; define res(x) {local obj res v = {x % md}; return v;}
    ; md = 0
    ; mat A[2,2] = {res(2), res(3), res(5), res(7)}
    ; md = 5
    ; print det(A)
    obj res {4}
    ; md = 6
    ; print det(A)
    obj res {5}

    ; /*
       * NOTE: if A had been a 3 x 3 or larger matrix, res_div(a,b) for
       * non-zero b would have had to be defined (assuming at least one
       * division is necessary); for consistent results when md is composite,
       * res_div(a,b) should be defined only when b and md are relatively
       * prime; there is no problem when md is prime.
       */

LIMITS
    none

LINK LIBRARY
    VALUE matdet(MATRIX *m)

SEE ALSO
    matdim, matmax, matmin, inverse

## Copyright (C) 1999,2021  Landon Curt Noll
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