Opened 7 years ago
Closed 4 years ago
#9505 closed defect (fixed)
coeff(f,x*y) does not work
Reported by:  zimmerma  Owned by:  burcin 

Priority:  critical  Milestone:  sage6.2 
Component:  symbolics  Keywords:  pynac 
Cc:  Merged in:  
Authors:  Paul Zimmermann  Reviewers:  Ralf Stephan 
Report Upstream:  N/A  Work issues:  
Branch:  06b3fc1 (Commits)  Commit:  06b3fc1ae37916b9a69842e7f148d252bad5069d 
Dependencies:  Stopgaps:  #12699 
Description
The following is ok:
sage: var('x,y,z') sage: f=x*y*z^2 sage: f.coeff(z^2) x*y
However the following is not:
sage: f.coeff(x*y) 0
Attachments (1)
Change History (20)
comment:1 Changed 7 years ago by
comment:2 Changed 7 years ago by
 Cc malb removed
 Component changed from commutative algebra to symbolics
 Keywords pynac added
 Owner changed from malb to burcin
I'm switching the component to symbolics
since the problem involves symbolic expressions.
It seems that we inherited this behavior from GiNaC:
ginsh  GiNaC Interactive Shell (ginac V1.5.7) __, _______ Copyright (C) 19992010 Johannes Gutenberg University Mainz, (__) *  Germany. This is free software with ABSOLUTELY NO WARRANTY. ._) i N a C  You are welcome to redistribute it under certain conditions. <' For details type `warranty;'. Type ?? for a list of help topics. > f = x*y*z^2; y*z^2*x > coeff(f, z^2,1); y*x > coeff(f, x*y,1); 0
I will report this to the ginaclist.
comment:3 Changed 6 years ago by
 Stopgaps set to #12699
comment:4 Changed 6 years ago by
Since I don't know how to fix this, at least I can point out some related facts.
Maxima does exactly the same thing as GINAC (and Sage):
sage: !maxima ;;; Loading #P"/Users/wstein/sage/install/sage5.0.beta2/local/lib/ecl/sbbsdsockets.fas" ;;; Loading #P"/Users/wstein/sage/install/sage5.0.beta2/local/lib/ecl/sockets.fas" ;;; Loading #P"/Users/wstein/sage/install/sage5.0.beta2/local/lib/ecl/defsystem.fas" ;;; Loading #P"/Users/wstein/sage/install/sage5.0.beta2/local/lib/ecl/cmp.fas" Maxima 5.24.0 http://maxima.sourceforge.net using Lisp ECL 11.1.1 Distributed under the GNU Public License. See the file COPYING. Dedicated to the memory of William Schelter. The function bug_report() provides bug reporting information. (%i1) f : x*y*z; (%o1) x y z (%i2) coeff(f, x); (%o2) y z (%i3) coeff(f, x*y); (%o3) 0
Maple raises an error in this case:
> f := x*y*z > ; f := x y z > coeff(f, x); y z > coeff(f, x*y); Error, invalid input: coeff received x*y, which is not valid for its 2nd argument, x
Mathematica does what you expect:
In[1]:= f := x*y*z; In[2]:= Coefficient[f,x] Out[2]= y z In[3]:= Coefficient[f,x*y] Out[3]= z
Sage multivariate polynomials (hence Singular) do what you expect:
sage: R.<x,y,z>=QQ[] sage: f = x*y*z^2 sage: f.coefficient(x) y*z^2 sage: f.coefficient(x*y) z^2
comment:5 Changed 6 years ago by
a possible fix would be that f.coeff(x^n*y^m)
automatically calls
f.coeff(x,n).coeff(y,m)
which gives the expected answer:
sage: var('x,y,z') (x, y, z) sage: f=x*y*z^2 sage: f.coeff(x,1).coeff(y,1) z^2
Paul
comment:6 Changed 6 years ago by
We might need to expand the expression before doing recursive calls to coefficient()
:
sage: var('x,y,z') (x, y, z) sage: g = x*y*(z^2 + y*z) sage: g.coeff(x,1).coeff(y,1) z
Compare to MMA:
In[12]:= Coefficient[x*y*(z^2 + y*z), x*y] 2 Out[12]= z
comment:7 Changed 4 years ago by
 Milestone changed from sage5.11 to sage5.12
Changed 4 years ago by
comment:8 Changed 4 years ago by
 Status changed from new to needs_review
attached is a temporary fix that calls coeff in turn for each term x^n
in s
.
In addition it checks the extra argument n
is only used for a single symbol.
Paul
comment:9 Changed 4 years ago by
 Milestone changed from sage6.1 to sage6.2
comment:10 Changed 4 years ago by
 Branch set to u/rws/ticket/9505
 Modified changed from 01/30/14 21:20:52 to 01/30/14 21:20:52
comment:11 Changed 4 years ago by
 Commit set to 850abdcc3ce6d76d04d2bf9cbefc6aa7a2aec603
 Status changed from needs_review to positive_review
Patch applies cleanly, looks good, tests OK in symbolics/
Not sure if the stopgap is still necessary. My tests were satisfying but hey.
New commits:
850abdc  trac 9505: coeff(f,x*y) does not work

comment:12 Changed 4 years ago by
 Commit changed from 850abdcc3ce6d76d04d2bf9cbefc6aa7a2aec603 to 0c57d9a12ff6c9ae2541700dd2aee59cdb31cefc
 Status changed from positive_review to needs_review
Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:
0c57d9a  Merge branch 'develop' into ticket/9505

comment:13 Changed 4 years ago by
 Status changed from needs_review to positive_review
comment:14 Changed 4 years ago by
 Reviewers set to Ralf Stephan
comment:15 Changed 4 years ago by
Documentation does not build
[calculus ] docstring of sage.symbolic.expression.Expression.coeff:57: WARNING: Literal block expected; none found. [calculus ] docstring of sage.symbolic.expression.Expression.coeff:57: WARNING: Literal block expected; none found. Traceback (most recent call last): File "/home/buildslavesage/slave/sage_git/build/src/doc/common/builder.py", line 83, in f execfile(sys.argv[0]) File "/home/buildslavesage/slave/sage_git/build/src/doc/common/customsphinxbuild.py", line 185, in <module> sphinx.cmdline.main(sys.argv) File "/home/buildslavesage/slave/sage_git/build/local/lib/python2.7/sitepackages/Sphinx1.1.2py2.7.egg/sphinx/cmdline.py", line 206, in main print >>error File "/home/buildslavesage/slave/sage_git/build/src/doc/common/customsphinxbuild.py", line 165, in write self._write(str) File "/home/buildslavesage/slave/sage_git/build/src/doc/common/customsphinxbuild.py", line 139, in _write self._log_line(line) File "/home/buildslavesage/slave/sage_git/build/src/doc/common/customsphinxbuild.py", line 108, in _log_line raise OSError(line) OSError: [calculus ] docstring of sage.symbolic.expression.Expression.coeff:57: WARNING: Literal block expected; none found.
comment:16 Changed 4 years ago by
sorry with the change to git I don't know how yet how to submit a patch, thus I won't be able to work on this in the near future.
Paul
comment:17 Changed 4 years ago by
 Commit changed from 0c57d9a12ff6c9ae2541700dd2aee59cdb31cefc to 06b3fc1ae37916b9a69842e7f148d252bad5069d
 Status changed from positive_review to needs_review
Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:
06b3fc1  Trac #9505: reviewer's patch: fix doc

comment:18 Changed 4 years ago by
 Status changed from needs_review to positive_review
comment:19 Changed 4 years ago by
 Branch changed from u/rws/ticket/9505 to 06b3fc1ae37916b9a69842e7f148d252bad5069d
 Resolution set to fixed
 Status changed from positive_review to closed
PS: I'm sorry if this is a duplicate. The trac search for "coeff" gives 295 entries!