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\sectionauthor{J\"org Lehmann}{joergl@users.sourceforge.net}
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With the \verb|unit| module \PyX{} makes available classes and
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functions for the specification and manipulation of lengths. As usual,
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lengths consist of a number together with a measurement unit, e.g.,
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\unit[1]{cm}, \unit[50]{points}, \unit[0.42]{inch}. In addition,
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lengths in \PyX{} are composed of the five types ``true'', ``user'',
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``visual'', ``width'', and ``\TeX'', e.g., \unit[1]{user cm},
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\unit[50]{true points}, $(0.42\ \mathrm{visual} + 0.2\
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\mathrm{width})$ inch. As their names indicate, they serve different
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purposes. True lengths are not scalable and are mainly used for return
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values of \PyX{} functions. The other length types can be rescaled by
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the user and differ with respect to the type of object they are
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\item[user length:] used for lengths of graphical objects like
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\item[visual length:] used for sizes of visual elements, like arrows,
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graph symbols, axis ticks, etc.
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\item[width length:] used for line widths
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\item[\TeX{} length:] used for all \TeX{} and \LaTeX{} output
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When not specified otherwise, all types of lengths are interpreted
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in terms of a default unit, which, by default, is \unit[1]{cm}.
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You may change this default unit by using the module level function
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\begin{funcdesc}{set}{uscale=None, vscale=None, wscale=None,
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xscale=None, defaultunit=None}
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When \var{uscale}, \var{vscale}, \var{wscale}, or \var{xscale} is not
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\keyword{None}, the corresponding scaling factor(s) is redefined to
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the given number. When \var{defaultunit} is not \keyword{None},
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the default unit is set to the given value, which has to be
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one of \code{"cm"}, \code{"mm"}, \code{"inch"}, or \code{"pt"}.
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For instance, if you only want thicker lines for a publication
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version of your figure, you can just rescale all width lengths using
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Or suppose, you are used to specify length in imperial units. In this,
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admittedly rather unfortunate case, just use
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unit.set(defaultunit="inch")
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at the beginning of your program.
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\section{Class length}
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\begin{classdesc}{length}{f, type="u", unit=None}
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The constructor of the \class{length} class expects as its first
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argument a number \var{f}, which represents the prefactor of the given length.
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By default this length is interpreted as a user length (\code{type="u"}) in units
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of the current default unit (see \function{set()} function of the \module{unit}
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module). Optionally, a different \var{type} may be specified, namely
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\code{"u"} for user lengths, \code{"v"} for visual lengths, \code{"w"}
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for width lengths, \code{"x"} for \TeX{} length, and \code{"t"} for true
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lengths. Furthermore, a different unit may be specified using the \var{unit}
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argument. Allowed values are \code{"cm"}, \code{"mm"}, \code{"inch"},
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Instances of the \class{length} class support addition and substraction either by another \class{length}
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or by a number which is then interpeted as being a user length in
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default units, multiplication by a number and division either by another
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\class{length} in which case a float is returned or by a number in which
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case a \class{length} instance is returned. When two lengths are
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compared, they are first converted to meters (using the currently set
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scaling), and then the resulting values are compared.
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\section{Predefined length instances}
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A number of \verb|length| instances are already predefined, which
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only differ in there values for \verb|type| and \verb|unit|. They are
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summarized in the following table
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\begin{tabular}{lll|lll}
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name & type & unit & name & type & unit\\
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\constant{m} & user & m & \constant{v\_m} & visual & m\\
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\constant{cm} & user & cm & \constant{v\_cm} & visual & cm\\
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\constant{mm} & user & mm & \constant{v\_mm} & visual & mm\\
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\constant{inch} & user & inch & \constant{v\_inch} & visual & inch\\
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\constant{pt} & user & points & \constant{v\_pt} & visual & points\\
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\constant{t\_m} & true & m & \constant{w\_m} & width & m\\
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\constant{t\_cm} & true & cm & \constant{w\_cm} & width & cm\\
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\constant{t\_mm} & true & mm & \constant{w\_mm} & width & mm\\
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\constant{t\_inch} & true & inch & \constant{w\_inch} & width & inch\\
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\constant{t\_pt} & true & points & \constant{w\_pt} & width & points\\
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\constant{u\_m} & user & m & \constant{x\_m} & \TeX & m \\
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\constant{u\_cm} & user & cm & \constant{x\_cm} & \TeX & cm \\
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\constant{u\_mm} & user & mm & \constant{x\_mm} & \TeX & mm \\
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\constant{u\_inch} & user & inch & \constant{x\_inch} & \TeX & inch \\
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\constant{u\_pt} & user & points & \constant{x\_pt} & \TeX & points\\
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Thus, in order to specify, e.g., a length of 5 width points, just use
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\section{Conversion functions}
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If you want to know the value of a \PyX{} length in certain units, you
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may use the predefined conversion functions which are given in the
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\texttt{tom(l)} & \texttt{l} in units of m\\
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\texttt{tocm(l)} & \texttt{l} in units of cm\\
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\texttt{tomm(l)} & \texttt{l} in units of mm\\
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\texttt{toinch(l)} & \texttt{l} in units of inch\\
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\texttt{topt(l)} & \texttt{l} in units of points\\
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If \verb|l| is not yet a \verb|length| instance but a number, it first
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is interpreted as a user length in the default units.
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