Pull out subfield() method from subfields() method.

[kwankyu]

It is currently clumsy to create a subfield of a finite field using subfields() method.

sage: k = GF(2^21)
sage: k.subfields(3)
[(Finite Field in z3 of size 2^3, Ring morphism:
    From: Finite Field in z3 of size 2^3
    To:   Finite Field in z21 of size 2^21
    Defn: z3 |--> z21^20 + z21^19 + z21^17 + z21^15 + z21^11 + z21^9 + z21^8 + z21^6 + z21^2)]
sage: K, _ = k.subfields(3)[0]
sage: K
Finite Field in z3 of size 2^3

With the patch of this ticket, we have subfield() method such that

sage: k = GF(2^21)
sage: k.subfield(3)
Finite Field in z3 of size 2^3
sage: K = _
sage: k.coerce_map_from(K)
Ring morphism:
  From: Finite Field in z3 of size 2^3
  To:   Finite Field in z21 of size 2^21
  Defn: z3 |--> z21^20 + z21^19 + z21^17 + z21^15 + z21^11 + z21^9 + z21^8 + z21^6 + z21^2

Component: finite rings

Author: Kwankyu Lee

Branch: bd8ba10

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/27949

[kwankyu]

Branch: u/klee/27949

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

87179a7

Pull out subfield() from subfields()

[sagetrac-git]

Commit: 87179a7

[embray]

comment:4

Moving tickets from the Sage 8.8 milestone that have been actively worked on in the last six months to the next release milestone (optimistically).

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

30e85b3

Merge branch 'develop'

[sagetrac-git]

Changed commit from 87179a7 to 30e85b3

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

147a412

Pull out subfield() from subfields()

[sagetrac-git]

Changed commit from 30e85b3 to 147a412

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:7

LGTM.

[tscrim]

comment:8

Sorry, I just noticed something:

return [self.subfields(m, name=name[m])[0] for m in divisors]

Couldn't this use your new subfield() method?

[kwankyu]

comment:9

Replying to @tscrim:

Sorry, I just noticed something:

return [self.subfields(m, name=name[m])[0] for m in divisors]

Couldn't this use your new subfield() method?

Then it would look like

-        return [self.subfields(m, name=name[m])[0] for m in divisors]
+
+        pairs = []
+        for m in divisors:
+            K =  self.subfield(m, name=name[m])
+            pairs.append( (K, self.coerce_map_from(K)) )
+        return pairs

It is somewhat duplicating the code above. Is this better?

[tscrim]

comment:10

Replying to @kwankyu:

Replying to @tscrim:

Sorry, I just noticed something:

return [self.subfields(m, name=name[m])[0] for m in divisors]

Couldn't this use your new subfield() method?

Then it would look like

-        return [self.subfields(m, name=name[m])[0] for m in divisors]
+
+        pairs = []
+        for m in divisors:
+            K =  self.subfield(m, name=name[m])
+            pairs.append( (K, self.coerce_map_from(K)) )
+        return pairs

It is somewhat duplicating the code above. Is this better?

Maybe. It seems less wasteful in terms of object creation and it is not too much code duplication. Plus, the current version almost seems to to go against the new method; although I guess not exactly from what you're saying.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

bd8ba10

Use subfield() in subfields() method

[sagetrac-git]

Changed commit from 147a412 to bd8ba10

[tscrim]

comment:13

Thank you.

[kwankyu]

comment:14

My pleasure. Thank you!

[fchapoton]

comment:15

moving milestone to 9.0 (after release of 8.9)

[vbraun]

Changed branch from u/klee/27949 to bd8ba10

[mkoeppe]

comment:17

Follow-up: #30171

[mkoeppe]

Changed commit from bd8ba10 to none