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 that 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  Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
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## Calc is distributed in the hope that it will be useful, but WITHOUT
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## or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
##
## Under source code control:	1995/11/28 11:17:47
## File existed as early as:	1995
##
## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
