#19552: images and preimages for projective subscheme
-------------------------------------+-------------------------------------
Reporter: bhutz | Owner: bhutz
Type: enhancement | Status: needs_work
Priority: minor | Milestone: sage-6.10
Component: algebraic | Resolution:
geometry | Merged in:
Keywords: subscheme | Reviewers: Vincent Delecroix
iteration | Work issues:
Authors: Ben Hutz | Commit:
Report Upstream: N/A | 45697b745f19b2387ed28afd7e787b84a4a238cb
Branch: | Stopgaps:
u/bhutz/ticket/19552 |
Dependencies: |
-------------------------------------+-------------------------------------
Changes (by vdelecroix):
* status: needs_review => needs_work
Comment:
- In your first commit, you completely removed the file
`schemes/generic/morphism.py`. Why is so?
- test the error that are raised. And to fit with Python standards that
was discussed on sage-devel, the error message should be lower case with
no ponctuation at the end like the following
{{{
sage: [][1]
Traceback (most recent call last):
...
IndexError: list index out of range
}}}
- change `if (isinstance(N,(list,tuple)) == False)` to `if not
isinstance(N, (list,tuple))`. Similarly, change `if normalize == True`
with `if normalize`.
- In
{{{
+ except TypeError:
+ raise TypeError("Orbit bounds must be integers")
}}}
or
{{{
+ except TypeError:
+ raise TypeError("Iterate number must be an integer")
}}}
there is no need to catch a `TypeError` to raise a `TypeError`.
- Why are you using a copy of `self` in `orbit`?
- `a proejctive subscheme` -> `projective`. Moreover the output is
'''not''' a projective subscheme but a list!
- What is this line in the documentation of `orbit`
{{{
Perform the checks on subscheme initialization if ``check=True``
}}}
- The mention to `self` in the documentation should be avoided as much as
possible. You can replace by `this scheme`.
- You can simplify a bit the following in `nth_iterate`
{{{
+ if n == 0:
+ return(self)
+ else:
+ Q = f(self)
+ for i in range(2,n+1):
+ Q = f(Q)
+ return(Q)
}}}
with
{{{
Q = self
for i in range(n):
Q = f(Q)
return Q
}}}
- to make a list of zeros use `[0] * n` instead of `[0 for _ in
range(n)]`.
- In `preimage` you wrote `return the subscheme` why is this unique? why
it does exist? The following looks fishy
{{{
sage: PS.<x,y,z> = ProjectiveSpace(ZZ, 2)
sage: H = End(PS)
sage: f = H([x^2, x^2, x^2])
sage: X = PS.subscheme([x-y])
sage: X.preimage(f)
Closed subscheme of Projective Space of dimension 2 over Integer Ring
defined by:
0
sage: f(X.preimage(f))
Closed subscheme of Projective Space of dimension 2 over Integer Ring
defined by:
y - z,
x - z
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/19552#comment:11>
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