(maxima.info)Introduction to Units

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87.1 Introduction to Units
==========================

The _unit_ package enables the user to convert between arbitrary units
and work with dimensions in equations.  The functioning of this package
is radically different from the original Maxima units package - whereas
the original was a basic list of definitions, this package uses rulesets
to allow the user to chose, on a per dimension basis, what unit final
answers should be rendered in.  It will separate units instead of
intermixing them in the display, allowing the user to readily identify
the units associated with a particular answer.  It will allow a user to
simplify an expression to its fundamental Base Units, as well as
providing fine control over simplifying to derived units.  Dimensional
analysis is possible, and a variety of tools are available to manage
conversion and simplification options.  In addition to customizable
automatic conversion, _units_ also provides a traditional manual
conversion option.

   Note - when unit conversions are inexact Maxima will make
approximations resulting in fractions.  This is a consequence of the
techniques used to simplify units.  The messages warning of this type of
substitution are disabled by default in the case of units (normally they
are on) since this situation occurs frequently and the warnings clutter
the output.  (The existing state of ratprint is restored after unit
conversions, so user changes to that setting will be preserved
otherwise.)  If the user needs this information for units, they can set
_unitverbose:on_ to reactivate the printing of warnings from the unit
conversion process.

   _unit_ is included in Maxima in the share/contrib/unit directory.  It
obeys normal Maxima package loading conventions:

     (%i1) load("unit")$
     *******************************************************************
     *                       Units version 0.50                        *
     *          Definitions based on the NIST Reference on             *
     *              Constants, Units, and Uncertainty                  *
     *       Conversion factors from various sources including         *
     *                   NIST and the GNU units package                *
     *******************************************************************

     Redefining necessary functions...
     WARNING: DEFUN/DEFMACRO: redefining function TOPLEVEL-MACSYMA-EVAL ...
     WARNING: DEFUN/DEFMACRO: redefining function MSETCHK ...
     WARNING: DEFUN/DEFMACRO: redefining function KILL1 ...
     WARNING: DEFUN/DEFMACRO: redefining function NFORMAT ...
     Initializing unit arrays...
     Done.

   The WARNING messages are expected and not a cause for concern - they
indicate the _unit_ package is redefining functions already defined in
Maxima proper.  This is necessary in order to properly handle units.
The user should be aware that if other changes have been made to these
functions by other packages those changes will be overwritten by this
loading process.

   The _unit.mac_ file also loads a lisp file _unit-functions.lisp_
which contains the lisp functions needed for the package.

   Clifford Yapp is the primary author.  He has received valuable
assistance from Barton Willis of the University of Nebraska at Kearney
(UNK), Robert Dodier, and other intrepid folk of the Maxima mailing
list.

   There are probably lots of bugs.  Let me know.  'float' and 'numer'
don't do what is expected.

   TODO : dimension functionality, handling of temperature, showabbr and
friends.  Show examples with addition of quantities containing units.