algebrite/sources/abs.coffee

Computer Algebra System in Coffeescript

# Absolute value, aka vector magnitude



Eval_abs = ->
	push(cadr(p1))
	Eval()
	absval()

absval = ->
	h = 0
	save()
	p1 = pop()

	if (istensor(p1))
		absval_tensor()
		restore()
		return

	if (isnum(p1))
		push(p1)
		if (isnegativenumber(p1))
			negate()
		restore()
		return

	if (iscomplexnumber(p1))
		push(p1)
		push(p1)
		conjugate()
		multiply()
		push_rational(1, 2)
		power()
		restore()
		return

	# abs(1/a) evaluates to 1/abs(a)

	if (car(p1) == symbol(POWER) && isnegativeterm(caddr(p1)))
		push(p1)
		reciprocate()
		absval()
		reciprocate()
		restore()
		return

	# abs(a*b) evaluates to abs(a)*abs(b)

	if (car(p1) == symbol(MULTIPLY))
		h = tos
		p1 = cdr(p1)
		while (iscons(p1))
			push(car(p1))
			absval()
			p1 = cdr(p1)
		multiply_all(tos - h)
		restore()
		return

	if (isnegativeterm(p1) || (car(p1) == symbol(ADD) && isnegativeterm(cadr(p1))))
		push(p1)
		negate()
		p1 = pop()

	push_symbol(ABS)
	push(p1)
	list(2)

	restore()

absval_tensor = ->
	if (p1.tensor.ndim != 1)
		stop("abs(tensor) with tensor rank > 1")
	push(p1)
	push(p1)
	conjugate()
	inner()
	push_rational(1, 2)
	power()
	simplify()
	Eval()