mag.cpp

/* Magnitude of complex z

	z		mag(z)
	-		------

	a		a

	-a		a

	(-1)^a		1

	exp(a + i b)	exp(a)

	a b		mag(a) mag(b)

	a + i b		sqrt(a^2 + b^2)

Notes

	1. Handles mixed polar and rectangular forms, e.g. 1 + exp(i pi/3)

	2. jean-francois.debroux reports that when z=(a+i*b)/(c+i*d) then

		mag(numerator(z)) / mag(denominator(z))

	   must be used to get the correct answer. Now the operation is
	   automatic.
*/

#include "stdafx.h"
#include "defs.h"

void
eval_mag(void)
{
	push(cadr(p1));
	eval();
	mag();
}

void
mag(void)
{
	save();
	p1 = pop();
	push(p1);
	numerator();
	yymag();
	push(p1);
	denominator();
	yymag();
	divide();
	restore();
}

void
yymag(void)
{
	save();
	p1 = pop();
	if (isnegativenumber(p1)) {
		push(p1);
		negate();
	} else if (car(p1) == symbol(POWER) && equaln(cadr(p1), -1))
		// -1 to a power
		push_integer(1);
	else if (car(p1) == symbol(POWER) && cadr(p1) == symbol(E)) {
		// exponential
		push(caddr(p1));
		real();
		exponential();
	} else if (car(p1) == symbol(MULTIPLY)) {
		// product
		push_integer(1);
		p1 = cdr(p1);
		while (iscons(p1)) {
			push(car(p1));
			mag();
			multiply();
			p1 = cdr(p1);
		}
	} else if (car(p1) == symbol(ADD)) {
		// sum
		push(p1);
		rect(); // convert polar terms, if any
		p1 = pop();
		push(p1);
		real();
		push_integer(2);
		power();
		push(p1);
		imag();
		push_integer(2);
		power();
		add();
		push_rational(1, 2);
		power();
		simplify_trig();
	} else
		// default (all real)
		push(p1);
	restore();
}

#if SELFTEST

static const char *s[] = {

	"mag(a+i*b)",
	"(a^2+b^2)^(1/2)",

	"mag(exp(a+i*b))",
	"exp(a)",

	"mag(1)",
	"1",

	"mag(-1)",
	"1",

	"mag(1+exp(i*pi/3))",
	"3^(1/2)",

	"mag((a+i*b)/(c+i*d))",
	"(a^2+b^2)^(1/2)/((c^2+d^2)^(1/2))",

	"mag(exp(i theta))",
	"1",

	"mag(exp(-i theta))",
	"1",

	"mag((-1)^theta)",
	"1",

	"mag((-1)^(-theta))",
	"1",

	"mag(3*(-1)^theta)",
	"3",

	"mag(3*(-1)^(-theta))",
	"3",

	"mag(-3*(-1)^theta)",
	"3",

	"mag(-3*(-1)^(-theta))",
	"3",
};

void
test_mag(void)
{
	test(__FILE__, s, sizeof s / sizeof (char *));
}

#endif