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% radix.htex
It is possible to expand numbers in general bases.

\xtc{
Here we expand \spad{111} in base \spad{5}.
This means
\begin{texonly}
$10^2+10^1+10^0 = 4 \cdot 5^2+2 \cdot 5^1 + 5^0.$
\end{texonly}
\begin{htonly}
\spad{10^2+10^1+10^0 = 4*5^2+2*5^1+5^0.}
\end{htonly}
}{
\spadcommand{111::RadixExpansion(5)}
}

\xtc{
You can expand fractions to form repeating expansions.
}{
\spadcommand{(5/24)::RadixExpansion(2)}
}
\xtc{
}{
\spadcommand{(5/24)::RadixExpansion(3)}
}
\xtc{
}{
\spadcommand{(5/24)::RadixExpansion(8)}
}
\xtc{
}{
\spadcommand{(5/24)::RadixExpansion(10)}
}
\xtc{
For bases from 11 to 36 the letters A through Z are used.
}{
\spadcommand{(5/24)::RadixExpansion(12)}
}
\xtc{
}{
\spadcommand{(5/24)::RadixExpansion(16)}
}
\xtc{
}{
\spadcommand{(5/24)::RadixExpansion(36)}
}
\xtc{
For bases greater than 36, the ragits are separated by blanks.
}{
\spadcommand{(5/24)::RadixExpansion(38)}
}
\xtc{
The \spadtype{RadixExpansion} type provides operations to obtain the
individual ragits.
Here is a rational number in base \spad{8}.
}{
\spadcommand{a := (76543/210)::RadixExpansion(8) \bound{a}}
}
\xtc{
The operation \spadfunFrom{wholeRagits}{RadixExpansion} returns a list of the
ragits for the integral part of the number.
}{
\spadcommand{w := wholeRagits a \free{a}\bound{w}}
}
\xtc{
The operations \spadfunFrom{prefixRagits}{RadixExpansion} and \spadfunFrom{cycleRagits}{RadixExpansion}
return lists of the initial and repeating ragits in the
fractional part of the number.
}{
\spadcommand{f0 := prefixRagits a \free{a}\bound{f0}}
}
\xtc{
}{
\spadcommand{f1 := cycleRagits a \free{a}\bound{f1}}
}
\xtc{
You can construct any radix expansion by giving the
whole, prefix and cycle parts.
The declaration is necessary to let \Language{}
know the base of the ragits.
}{
\spadcommand{u:RadixExpansion(8):=wholeRadix(w)+fractRadix(f0,f1) \free{w f0 f1}\bound{u}}
}
\xtc{
If there is no repeating part, then the list \spad{[0]} should be used.
}{
\spadcommand{v: RadixExpansion(12) := fractRadix([1,2,3,11], [0]) \bound{v}}
}
\xtc{
If you are not interested in the repeating nature of the expansion,
an infinite stream of ragits can be obtained using
\spadfunFrom{fractRagits}{RadixExpansion}.
}{
\spadcommand{fractRagits(u) \free{u}}
}
\xtc{
Of course, it's possible to recover the fraction representation:
}{
\spadcommand{a :: Fraction(Integer) \free{a}}
}

\showBlurb{RadixExpansion}
More examples of expansions are available in
\xmpref{DecimalExpansion},
\xmpref{BinaryExpansion}, and
\xmpref{HexadecimalExpansion}.
