algebrite/sources/cofactor.coffee

Computer Algebra System in Coffeescript

### cofactor =====================================================================

Tags
----
scripting, JS, internal, treenode, general concept

Parameters
----------
m,i,j

General description
-------------------
Cofactor of a matrix component.
Let c be the cofactor matrix of matrix m, i.e. tranpose(c) = adj(m).
This function returns c[i,j].

###


Eval_cofactor = ->

	i = 0
	j = 0
	n = 0
	push(cadr(p1))
	Eval()
	p2 = pop()
	if (istensor(p2) && p2.tensor.ndim == 2 && p2.tensor.dim[0] == p2.tensor.dim[1])
		doNothing = 1
	else
		stop("cofactor: 1st arg: square matrix expected")
	n = p2.tensor.dim[0]
	push(caddr(p1))
	Eval()
	i = pop_integer()
	if (i < 1 || i > n)
		stop("cofactor: 2nd arg: row index expected")
	push(cadddr(p1))
	Eval()
	j = pop_integer()
	if (j < 1 || j > n)
		stop("cofactor: 3rd arg: column index expected")
	cofactor(p2, n, i - 1, j - 1)

cofactor = (p, n, row, col) ->
	i = 0
	j = 0
	for i in [0...n]
		for j in [0...n]
			if (i != row && j != col)
				push(p.tensor.elem[n * i + j])
	determinant(n - 1)
	if ((row + col) % 2)
		negate()