Opened 11 years ago
Closed 8 years ago
#7712 closed defect (duplicate)
error with polynomial with interval coefficients
Reported by: | zimmerma | Owned by: | AlexGhitza |
---|---|---|---|
Priority: | major | Milestone: | sage-duplicate/invalid/wontfix |
Component: | basic arithmetic | Keywords: | |
Cc: | kohel | Merged in: | |
Authors: | Reviewers: | Travis Scrimshaw | |
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | #13760 | Stopgaps: |
Description (last modified by )
Consider the following example:
sage: P.<y,z> = PolynomialRing(RealIntervalField(2)) sage: Q.<x> = PolynomialRing(P) sage: C = (y-x)^3 sage: C(y/2) 0
I do not understand why the result is 0. In fact there are two errors: (i) the result is a polynomial of degree 3 in y, thus y^{3} should appear (ii) the result should "contain" the exact result which is 0.125*y^{3}, thus it should be c*y^{3} where c is an interval containing 0.125. Compare the following with a precision of 10 bits:
sage: P.<y,z> = PolynomialRing(RealIntervalField(10)) sage: Q.<x> = PolynomialRing(P) sage: C = (y-x)^3 sage: C(y/2) 0.12500?*y^3
Attachments (1)
Change History (19)
comment:1 Changed 11 years ago by
comment:2 Changed 11 years ago by
- Summary changed from error in polynomial substitution with interval coefficients to error in printing interval coefficients (together with variables)
Indeed:
sage: R=RealIntervalField(2) sage: r=R(-0.00,0.25) sage: r.str(style='brackets') '[-0.00 .. 0.25]' sage: r 1.? sage: r*x 0
I thus changed the summary.
comment:3 follow-up: ↓ 6 Changed 11 years ago by
- Summary changed from error in printing interval coefficients (together with variables) to error with polynomial with interval coefficients
Here is a more complex example, which shows this is not only a printing issue:
def method2(prec): n=[0,9,7,8,11,6,3,7,6,6,4,3,4,1,2,2,1,1,1,2,0,0,0,3,0,0,0,0,1] R = RealIntervalField(prec) P.<xk1,sk1,sk2> = PolynomialRing(R) Q.<xk> = PolynomialRing(P) C = (sk1-xk)^n[1]*xk^n[2] C=C.integral() C=C(sk1/2)-C(xk1) C=R(10^6)*C.subs(sk1=sk2-xk1) C=C.subs(xk1=xk,sk2=sk1) for k in range(3,29): C=C*xk^n[k] C=C.integral() C=C(sk1/k)-C(xk1) C=R(10^6)*C.subs(sk1=sk2-xk1) C=C.subs(xk1=xk,sk2=sk1) C=C.subs(xk=R(0),sk1=R(1)) return C(0,0,0) sage: method2(391) 0 sage: _.parent() Integer Ring sage: method2(392) 1.?e-8 sage: _.parent() Real Interval Field with 392 bits of precision
Normally, both calls should return an object of type "Real Interval Field", isn't it? (If necessary, I can open a different trac ticket for both issues.)
comment:4 Changed 11 years ago by
- Milestone changed from sage-4.3 to sage-4.3.1
I'm declaring a total feature freeze on sage-4.3.
comment:5 Changed 11 years ago by
Still there in 4.3.1.
comment:6 in reply to: ↑ 3 Changed 11 years ago by
- Summary changed from error with polynomial with interval coefficients to _
Replying to zimmerma:
C=C.subs(xk=R(0),sk1=R(1))
The two polynomials obtained here are constants. The strange behaviour about the type comes from line 153 of
sage/rings/polynomial/multi_polynomial_element.py
where we find:
try: K = x[0].parent() <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< except AttributeError: K = self.parent().base_ring() y = K(0) for (m,c) in self.element().dict().iteritems(): y += c*misc.mul([ x[i]**m[i] for i in range(n) if m[i] != 0])
I don't know exactly why, but It first try to take the type of the first input (here Integer 0) and this type is then changed only by coercion when doing the computation.
With precision 391 the polynomial is null and no operations are performed, so the results stays Integer.
I would say this is a bug but maybe there is a purpose behind this.
comment:7 Changed 11 years ago by
- Summary changed from _ to error with polynomial with interval coefficients
comment:8 follow-up: ↓ 9 Changed 11 years ago by
- Cc kohel added
Yann, are you sure this method call is called? I've added a print statement before
y=K(0)
and nothing is printed (in 4.3.3). I add David in cc, maybe he can help us.
comment:9 in reply to: ↑ 8 Changed 11 years ago by
Sorry, my last comment was not clear. The method call is called when you do return C(0,0,0)
.
comment:10 Changed 11 years ago by
Sorry, my last comment was not clear. The method call is called when you do return C(0,0,0).
with C(0,0,0)
I see no problem:
sage: P.<y,z> = PolynomialRing(RealIntervalField(2)) sage: Q.<x> = PolynomialRing(P) sage: C = (y-x)^3 sage: a=C(0,0,0) sage: type(a) <type 'sage.rings.real_mpfi.RealIntervalFieldElement'> sage: a.lower() 0.00 sage: a.upper() 0.00
comment:11 Changed 11 years ago by
Here is my point:
sage: def method2(prec): ....: n=[0,9,7,8,11,6,3,7,6,6,4,3,4,1,2,2,1,1,1,2,0,0,0,3,0,0,0,0,1] ....: R = RealIntervalField(prec) ....: P.<xk1,sk1,sk2> = PolynomialRing(R) ....: Q.<xk> = PolynomialRing(P) ....: C = (sk1-xk)^n[1]*xk^n[2] ....: C=C.integral() ....: C=C(sk1/2)-C(xk1) ....: C=R(10^6)*C.subs(sk1=sk2-xk1) ....: C=C.subs(xk1=xk,sk2=sk1) ....: for k in range(3,29): ....: C=C*xk^n[k] ....: C=C.integral() ....: C=C(sk1/k)-C(xk1) ....: C=R(10^6)*C.subs(sk1=sk2-xk1) ....: C=C.subs(xk1=xk,sk2=sk1) ....: C=C.subs(xk=R(0),sk1=R(1)) ....: return C ....: sage: C391 = method2(391) sage: C391 0 sage: type(C391) <class 'sage.rings.polynomial.multi_polynomial_element.MPolynomial_polydict'> sage: type(C391(0,0,0)) <type 'sage.rings.integer.Integer'> sage: type(C391(GF(17)['z'](0),0,0)) <type 'sage.rings.polynomial.polynomial_zmod_flint.Polynomial_zmod_flint'>
comment:12 Changed 11 years ago by
Here is my point: [...]
ok, I thought you were speaking about the first (smaller) examples. I can reduce this second problem to the following:
sage: R.<x,y> = PolynomialRing(RR) sage: f=R(1); type(f(0,0)) <type 'sage.rings.real_mpfr.RealNumber'> sage: f=R(0); type(f(0,0)) <type 'sage.rings.integer.Integer'>
David, please can you explain why it is so?
comment:13 Changed 8 years ago by
I didn't see this ticket when submitting the new ticket #13760. There I provide a patch that corrects this bug. The two tickets should be merged (and probably closed after review of the patch).
comment:14 Changed 8 years ago by
- Description modified (diff)
comment:15 Changed 8 years ago by
- Status changed from new to needs_review
comment:16 Changed 8 years ago by
- Dependencies set to #13760
I propose to mark this as "duplicate", since #13760 solves that issue.
Paul
comment:17 Changed 8 years ago by
- Milestone changed from sage-5.6 to sage-duplicate/invalid/wontfix
- Reviewers set to Travis Scrimshaw
- Status changed from needs_review to positive_review
Hey Paul and Guillaume,
For future reference, just mark the patch as duplicate in the milestone dropdown and set it to needs_review.
#13760 does seem to fix the problem:
sage: method2(391) 0.?e-8 sage: _.parent() Real Interval Field with 391 bits of precision
Best,
Travis
comment:18 Changed 8 years ago by
- Resolution set to duplicate
- Status changed from positive_review to closed
It seems it just a printing issue: