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<a name="Introduction-to-Units"></a>
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<p>
Next: <a href="maxima_260.html#Functions-and-Variables-for-Units" accesskey="n" rel="next">Functions and Variables for Units</a>, Previous: <a href="maxima_258.html#unit_002dpkg" accesskey="p" rel="previous">unit-pkg</a>, Up: <a href="maxima_258.html#unit_002dpkg" accesskey="u" rel="up">unit-pkg</a> [<a href="maxima_toc.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="maxima_264.html#g_t_0423_043a_0430_0437_0430_0442_0435_043b_044c-_0444_0443_043d_043a_0446_0438_0439-_0438-_043f_0435_0440_0435_043c_0435_043d_043d_044b_0445" title="Index" rel="index">Index</a>]</p>
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<a name="Introduction-to-Units-1"></a>
<h3 class="section">72.1 Introduction to Units</h3>
<p>The <em>unit</em> 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, <em>units</em> also provides a traditional manual
conversion option.
</p>
<p>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
<em>unitverbose:on</em> to reactivate the printing of warnings from the unit
conversion process.
</p>
<p><em>unit</em> is included in Maxima in the share/contrib/unit directory. It obeys
normal Maxima package loading conventions:
</p>
<div class="example">
<pre class="example">(%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.
</pre></div>
<p>The WARNING messages are expected and not a cause for concern - they indicate
the <em>unit</em> 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.
</p>
<p>The <em>unit.mac</em> file also loads a lisp file <em>unit-functions.lisp</em> which
contains the lisp functions needed for the package.
</p>
<p>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.
</p>
<p>There are probably lots of bugs. Let me know. <code>float</code> and <code>numer</code>
don’t do what is expected.
</p>
<p>TODO : dimension functionality, handling of temperature,
showabbr and friends. Show examples with addition of quantities containing
units.
</p>
<a name="Item_003a-unit_002fnode_002fFunctions-and-Variables-for-Units"></a><hr>
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Next: <a href="maxima_260.html#Functions-and-Variables-for-Units" accesskey="n" rel="next">Functions and Variables for Units</a>, Previous: <a href="maxima_258.html#unit_002dpkg" accesskey="p" rel="previous">unit-pkg</a>, Up: <a href="maxima_258.html#unit_002dpkg" accesskey="u" rel="up">unit-pkg</a> [<a href="maxima_toc.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="maxima_264.html#g_t_0423_043a_0430_0437_0430_0442_0435_043b_044c-_0444_0443_043d_043a_0446_0438_0439-_0438-_043f_0435_0440_0435_043c_0435_043d_043d_044b_0445" title="Index" rel="index">Index</a>]</p>
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