Singular 2-0-4 Manual: 4.8 map

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4.8 map

Maps are ring maps from a preimage ring into the basering.

Note:

the target of a map is ALWAYS the actual basering
the preimage ring is stored "by name", that means, maps can only be used in such contexts, where the name of the preimage ring can be resolved (i.e., there might be problems for rings/maps defined in subprocedures). See also Identifier resolution, Names in procedures.

Maps between rings with different coefficient fields are possible and listed below.

Canonically realized are

$Q \rightarrow Q(a, \ldots)$
$Q \rightarrow R$
$Q \rightarrow C$
$Z/p \rightarrow (Z/p)(a, \ldots)$
$Z/p \rightarrow GF(p^n)$
$Z/p \rightarrow R$
$R \rightarrow C$

Possible are furthermore

$Z/p \rightarrow Q, \quad [i]_p \mapsto i \in [-p/2, \, p/2] \subseteq Z$
$Z/p \rightarrow Z/p^\prime, \quad [i]_p \mapsto i \in [-p/2, \, p/2] \subseteq Z, \; i \mapsto [i]_{p^\prime} \in Z/p^\prime$
$C \rightarrow R, \quad$ the real part

Finally, in Singular we allow the mapping from rings with coefficient field Q to rings whose ground fields have finite characteristic:

$Q \rightarrow Z/p$
$Q \rightarrow (Z/p)(a, \ldots)$

In these cases the denominator and the numerator of a number are mapped separately by the usual map from Z to Z/p, and the image of the number is built again afterwards by division. It is thus not allowed to map numbers whose denominator is divisible by the characteristic of the target ground field, or objects containing such numbers. We, therefore, strongly recommend using such maps only to map objects with integer coefficients.

4.8.1 map declarations

4.8.2 map expressions

4.8.3 map operations

5.1.31 fetch

5.1.48 imap

5.1.124 subst

See imap; fetch; subst.

User manual for Singular version 2-0-4, October 2002, generated by texi2html.