/*
 * Copyright (c) 1995, 1996 Gunther Schadow.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#ifndef PG_BASEUNIT_H_
#define PG_BASEUNIT_H_

#include <pg_config.h>
#include <iostream.h>

#pragma interface

/*---------------------------------------------------------------------------
THE VECTOR OF BASIC MEASURES

This file defines the struct base_unit_vector.  The base unit vector
tries to enclose any mesured phenomena and thereby tries to be
minimal.  The elements of the base unit vector are interger numbers
which denote the exponent under which the corresponding basic measure
counts to the derived measure. Consider a simple base vector [L, T]
that is made up only of length (L) and time (T), at least the
following measures can be expressed:

  Measure	Vector
  ------------- -------
  1		[ 0, 0]
  length	[ 1, 0]
  area		[ 2, 0]
  volume	[ 3, 0]
  time		[ 0, 1]
  velocity	[ 1,-1]
  acceleration	[ 1,-2]
  fluid current	[ 3,-1]
  ...		...

The operations on these classes of vectors are: Addition and
subtraction, which means multiplication resp. division of measures;
and multiplication of a vector with a scalar (integer) n which means
the n-th potence of the measure. The example below shows the
calculation of the acceleration vector:

   acceleration = length  / time    ^ 2
   		= [ 1, 0] - [ 0, 1] * 2
		= [ 1, 0] - [ 0, 2]
		= [ 1,-2]

Minimality is the reason why the concept of SI base units had to be
left almost completely. SI base units are the following:

  Measure			Unit
  ----------------------------- ------- -----------
  length			m	meter
  mass				kg	kilogram
  time				s	second
  electric current		A	Amp`ere
  thermodynamic temperature	K	Kelvin
  amount of substance		mol	mole
  luminous intensity		cd	candela

While there are no problems with length, time and temperature, it is
certainly not useful to have a prefix `kilo' in a base unit as it is
the case with mass. The reason for this is consistency with the rules
of prefixing: If we would accept kg as a base unit, we had to allow

	1kkg = 1Mg

and
	1mkg = 1g

which is certainly not correct. Thus I decided to use the Gram as the
base unit for mass.

It might be just for my personal taste that I use the charge as the
base unit of electrical phenomena instead of currency: it is the
electron resp. the elementary *charge* that all electical phenomena
are based on.

Since the amount of substance represents just the number of particles,
it is in fact a dimensionless measure (see The Feynman Lecutres on
Physics p.39-10??). The mole will therefore be defined later as a
pseudo-unit equal to avogadro's number.

Finally, I am not yet finished with luminous intensity and I am
thinking about dropping it as a base unit. Since the luminous
phenomenon is either just another electromagnetic phenomenon or it
belongs into the sensory physiology just like the intensity of
sound. Since I'm not yet aware of the implications of the candela as a
base unit, I'll leave it untouched for the time being.

The following table shows the basic measures as I will use them here:

  Measure			Unit
  ----------------------------- ------- -----------
  length			m	meter
  time         			s	second
  mass         			g 	gram
  electrical charge		C	Coulomb
  termodynamic temperature	K	Kelvin
  luminous intensity		cd	candela   
  angle				circ	Circle

As can be seen, I admitted the angle to the list of basic measures.
Otherwise I see no way how to be aware of the incommensurability of
steradian and radian (1sr = rad^2).  The angle is measured in
whole circles, thus 360deg = 1circ is true.  By this way, there is
something that can be considered as a law of nature that describes
relation of radius (r), length of the bow (b) and angle (phi):

	b[m] = P[1/circ] * phi[circ] * r[m]

with the constant P:

	     (2pi)m
	P = ---------- = (2pi)/circ
	    1circ / 1m

---------------------------------------------------------------------------*/

struct base_unit_vector
{
  int length       :8; // Length in 1m (Meter)
  int time         :8; // Time in 1s (Second)
  int mass         :8; // Mass in 1g (Gram)
  int charge       :8; // Electrical charge in 1C (Coulomb)
  int temperature  :8; // Thermodynamic temperature in 1K (Kelvin)
  int lumin_intens :8; // Luminous intensity in 1cd (Candela)   
  int angle        :8; // Angle in 1circ (Circle)

  base_unit_vector operator + (const base_unit_vector&) const;
  base_unit_vector operator - (const base_unit_vector&) const;
  base_unit_vector operator - () const;
  base_unit_vector& operator += (const base_unit_vector&);
  base_unit_vector& operator -= (const base_unit_vector&);

  base_unit_vector  operator * (int x) const;
  base_unit_vector& operator *= (int x);

  bool operator == (const base_unit_vector&) const;
  bool operator != (const base_unit_vector&) const;

  ostream& show(ostream &) const;
};

#ifndef OUTLINE
# include "BaseUnit.icc"
#endif

#endif /* !PG_BASEUNIT_H_ */