Opened 6 years ago
Closed 3 years ago
#15786 closed defect (worksforme)
floor fails for certain expressions.
Reported by:  fwclarke  Owned by:  

Priority:  major  Milestone:  sageduplicate/invalid/wontfix 
Component:  symbolics  Keywords:  floor 
Cc:  Merged in:  
Authors:  Reviewers:  Jeroen Demeyer  
Report Upstream:  N/A  Work issues:  
Branch:  u/deinst/15786floor (Commits)  Commit:  16e522fb6876ce646af7c52348056b94f3b8dfbc 
Dependencies:  Stopgaps: 
Description
x = (1725033*pi  5419351)/(25510582*pi  80143857) sage: floor(x)  ValueError Traceback (most recent call last) <ipythoninput400b214ffda37c2> in <module>() > 1 floor(x) /Users/mafwc/sage6.1/local/lib/python2.7/sitepackages/sage/functions/other.pyc in __call__(self, x, maximum_bits) 579 try: 580 x_interval = RealIntervalField(bits)(x) > 581 upper_floor = x_interval.upper().floor() 582 lower_floor = x_interval.lower().floor() 583 /Users/mafwc/sage6.1/local/lib/python2.7/sitepackages/sage/rings/real_mpfr.so in sage.rings.real_mpfr.RealNumber.floor (sage/rings/real_mpfr.c:17150)() ValueError: Calling floor() on infinity or NaN
The problem is that in this case x_interval.upper()
is infinite at line 581 of sage/functions/other.py:
sage: RealIntervalField(53)(x) [1.2500000000000000 .. +infinity]
A simple change to deal with this possibility should fix it.
Change History (17)
comment:1 Changed 6 years ago by
 Branch set to u/mmezzarobba/15786floor
 Commit set to 5a639167fd546ae48e212f82b868a0204c9cf119
comment:2 Changed 6 years ago by
 Commit changed from 5a639167fd546ae48e212f82b868a0204c9cf119 to abbd1464a6fc770478446a106d25876523974822
Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:
abbd146  Trac #15786: Initial fix, TBI

comment:3 followup: ↓ 4 Changed 6 years ago by
The new code seems to work well. But unfortunately I'm unable to test this fully because I can't currently rebuild sage. A few comments:
 It would be good practice to use
xrange
rather thanrange
 The
unique_floor
method for Real Interval Field elements can be used to simplify the code. Thus that the key part could read:for bits in xrange(53, maximum_bits, 100): try: return RealIntervalField(bits)(x).unique_floor() except ValueError: continue
 Corresponding changes should be made for the
ceil
function.  Doctests will, of course, be needed.
comment:4 in reply to: ↑ 3 ; followup: ↓ 5 Changed 6 years ago by
Thnaks for your comments.
Replying to fwclarke:
 It would be good practice to use
xrange
rather thanrange
I wasn't too sure about that as the correponding range will always be very short, but why not.
 The
unique_floor
method for Real Interval Field elements can be used to simplify the code.
Good point, thanks!
 Corresponding changes should be made for the
ceil
function.
Sure. And we should make sure that round()
does the right thing too.
I would also be tempted to double the precision each time the comparison is inconclusive, instead of increasing it by a fixed amount (at least for large values of bits
). In many cases, the complexity of RealIntervalField(bits)(x)
will be roughly linear in bits
, so the total running time wrt the necessary precision would drop from essentially quadratic to essentially linear. What do you think?
comment:5 in reply to: ↑ 4 Changed 6 years ago by
Replying to mmezzarobba:
Replying to fwclarke:
 It would be good practice to use
xrange
rather thanrange
I wasn't too sure about that as the correponding range will always be very short, but why not
I agree, but it would prevent a user wasting time by giving a ridiculously large value to maximum_bits
.
 Corresponding changes should be made for the
ceil
function.Sure. And we should make sure that
round()
does the right thing too.
Yes.
I would also be tempted to double the precision each time the comparison is inconclusive, instead of increasing it by a fixed amount (at least for large values of
bits
). In many cases, the complexity ofRealIntervalField(bits)(x)
will be roughly linear inbits
, so the total running time wrt the necessary precision would drop from essentially quadratic to essentially linear. What do you think?
Sounds convincing, but I'm no expert on interval arithmetic.
comment:6 Changed 6 years ago by
 Milestone changed from sage6.2 to sage6.3
comment:7 Changed 6 years ago by
 Milestone changed from sage6.3 to sage6.4
comment:8 Changed 5 years ago by
 Branch changed from u/mmezzarobba/15786floor to u/deinst/15786floor
comment:9 Changed 5 years ago by
 Commit changed from abbd1464a6fc770478446a106d25876523974822 to 16e522fb6876ce646af7c52348056b94f3b8dfbc
Ok, this updates the above fix so that it merges with a recent sage.
It also incorporates the review suggestions.
Both ceil
and floor
have FIXME:
notes saying to move the guts of __call__
to _eval_
. I'm willing to do that if it is only a cosmetic change, but I have next to no idea about what is going on with the dispatching.
New commits:
16e522f  17059 Ported the old fix to sage 6.7

comment:10 Changed 5 years ago by
 Milestone changed from sage6.4 to sage6.8
 Status changed from new to needs_review
comment:11 Changed 5 years ago by
 Component changed from basic arithmetic to symbolics
comment:12 followup: ↓ 13 Changed 5 years ago by
OK, I think I've figured out why no one has moved the code from __call__
to _eval
. If we do the replacement (returning None if we cannot simplify) then if we call ceil
or floor
with a nonnumeric argument then BuiltinFunction.__call__
delegates to Function.__call__
which coerces its result to an expression as follows
return new_Expression_from_GEx(SR, res)
So the result of floor
or ceil
is an expression (that consists of just an integer.)
At first glance, this seems harmless enough, but for to coerce an expression into an integer we call floor
or ceil
, and that wont work if floor
or ceil
is not returning an integer then we don't accomplish much. Although the Expression
object has an is_integer
method, it does not seem to have any way of getting that integer other than calling floor
or ceil
.
comment:13 in reply to: ↑ 12 Changed 5 years ago by
Just to complete the picture:
Replying to deinst:
... Although the
Expression
object has anis_integer
method, it does not seem to have any way of getting that integer other than callingfloor
orceil
.
This calls Pynac and performs a call to ex::info(info_flags::integer)
which is virtual so you have methods named info()
for all subclasses of basic
, see http://www.ginac.de/tutorial/#Theclasshierarchy. In fact, only add
, mul
, and numeric
have any handling of that flag, the relevant code is here:
 https://github.com/pynac/pynac/blob/master/ginac/add.cpp#L263
 https://github.com/pynac/pynac/blob/master/ginac/mul.cpp#L469
 https://github.com/pynac/pynac/blob/master/ginac/numeric.cpp#L1101
The last calls back Sage's function symbolic/pynac.pyx:cdef public bint py_is_integer()
which is
return isinstance(x, int) or isinstance(x, long) or isinstance(x, Integer) or \ (isinstance(x, Element) and ((<Element>x)._parent.is_exact() or (<Element>x)._parent == ring.SR) and (x in ZZ))
So, no, is_integer
does not call ceil
or floor
.
comment:14 followup: ↓ 15 Changed 5 years ago by
 Status changed from needs_review to needs_work
After a bit of thought, it seemed like the best thing to do would be to move the guts to _eval_
and replace __call__
with something like
def __call__(self, *args, **kwds): res = super(Function_floor, self).__call__(*args, **kwds) # Convert to Integer if the output was of type "int" and any of # the inputs was a Sage Element if isinstance(res, Expression) and res.is_integer(): return res.pyobject() else: return res
This should please everyone that expects floor to return an integer type instead of an expression type, while having the functionality routed in the standard way. Unforturnately, we now run into coersion problems on the other end, people are calling floor
with values that BuiltinFunction
cannot handle. For example, in prime_pi.py
there is a doctest
sage: prime_pi._eval_(str(2^100))
Which ends up taking floor(str(2^100))
. This works in the current implementation, as str(2^100)
can be coerced to an element of RealIntervalField
, but if we route the call through BuiltinFunction.__call__
it dies because str(2^100)
cannot be coerced to an element of SR
(this somewhat surprises me).
The obvious answer would be to add some coersion at the front of Function_floor.__call__
, but I don't know how far we should take treating floor
and ceil
as functions needing special care and handling.
There is still the problem of a potential infinite loop in the recursive call
return floor(SR(x).full_simplify().canonicalize_radical())
I don't know of any Expression
s that evaluate to integers, but that maxima
cannot simplify, but I'd be surprised if they don't exist. I'm still rummaging about on the border of pynac
to figure out how to stop the recursion. If nothing else I can use the substitute trick, but that seems too kludgy.
comment:15 in reply to: ↑ 14 Changed 5 years ago by
comment:16 Changed 4 years ago by
See also #12121.
comment:17 Changed 3 years ago by
 Milestone changed from sage6.8 to sageduplicate/invalid/wontfix
 Resolution set to worksforme
 Reviewers set to Jeroen Demeyer
 Status changed from needs_work to closed
This works in Sage 8.1.beta3
New commits:
Trac #15786: Initial fix, TBI