Opened 12 years ago
Closed 6 years ago
#6102 closed enhancement (fixed)
cohomology ring of simplicial complexes
Reported by:  bantieau  Owned by:  bantieau 

Priority:  major  Milestone:  sage6.10 
Component:  algebraic topology  Keywords:  
Cc:  jhpalmieri, fbreuer, tscrim, chapoton  Merged in:  
Authors:  John Palmieri, Travis Scrimshaw  Reviewers:  Travis Scrimshaw, John Palmieri 
Report Upstream:  N/A  Work issues:  
Branch:  9bfc2d2 (Commits, GitHub, GitLab)  Commit:  9bfc2d2881810588de6eb1ad85870a7ac95a1b28 
Dependencies:  #19179  Stopgaps: 
Description (last modified by )
Attachments (1)
Change History (53)
comment:1 Changed 10 years ago by
 Report Upstream set to N/A
comment:2 Changed 10 years ago by
 Cc fbreuer added
comment:3 Changed 8 years ago by
 Milestone changed from sage5.11 to sage5.12
comment:4 Changed 8 years ago by
 Milestone changed from sage6.1 to sage6.2
comment:5 Changed 7 years ago by
 Milestone changed from sage6.2 to sage6.3
comment:6 Changed 7 years ago by
 Milestone changed from sage6.3 to sage6.4
comment:7 Changed 6 years ago by
 Dependencies set to #19179
comment:8 Changed 6 years ago by
 Branch set to u/jhpalmieri/ATmodel
comment:9 Changed 6 years ago by
 Cc tscrim chapoton added
 Commit set to 763a8a8a03921e5198a8d51dbd61cc12ff0edcbc
 Status changed from new to needs_review
comment:10 Changed 6 years ago by
 Commit changed from 763a8a8a03921e5198a8d51dbd61cc12ff0edcbc to c0918b809f2f7ec04b87b75f218e132061bcf782
comment:11 Changed 6 years ago by
 Priority changed from minor to major
comment:12 Changed 6 years ago by
 Commit changed from c0918b809f2f7ec04b87b75f218e132061bcf782 to 6cd5b7ce9415262fef8c2402130273e159d7607f
Branch pushed to git repo; I updated commit sha1. New commits:
d65ba8d  trac 19179: change _repr_ for chain maps, chain homotopies

c38751b  Merge branch 'chains' into ATmodel

f70e3a2  trac 19179: doctest fixes for _repr_ changes

92b17e8  Merge branch 'chains' into ATmodel

6cd5b7c  trac 6102: doctest fixes for _repr_ changes

comment:13 Changed 6 years ago by
 Description modified (diff)
comment:14 Changed 6 years ago by
 Commit changed from 6cd5b7ce9415262fef8c2402130273e159d7607f to 869636b6ad5287ddaaf8657421d06e52a47194f3
comment:15 Changed 6 years ago by
#18246 broke the default hashing of chain homotopies, so I've added a __hash__
method, and also one for chain maps. This is necessary so that we can cache the methods algebraic_topological_model
, homology_basis
, and cohomology_ring
in cell_complex
.
comment:16 Changed 6 years ago by
 Commit changed from 869636b6ad5287ddaaf8657421d06e52a47194f3 to 5923e23d857ecdda88cd84d8b70d0ea2228acbde
comment:17 Changed 6 years ago by
An update: I have a new version of algebraic_topological_model.py
, which is the key to everything here. I'm calling it AT_model.py
, and I'll attach it to the ticket. The good news:
 it works for Delta complexes
 it's faster with mod 2 coefficients:
sage: from sage.homology.algebraic_topological_model import algebraic_topological_model sage: from sage.homology.AT_model import AT_model sage: RP3 = simplicial_complexes.RealProjectiveSpace(3) sage: %time phi, H = algebraic_topological_model(RP3, GF(2)) # old version CPU times: user 813 ms, sys: 150 ms, total: 963 ms Wall time: 852 ms sage: %time phi, H = AT_model(RP3, GF(2)) # new version CPU times: user 345 ms, sys: 32.3 ms, total: 377 ms Wall time: 354 ms
The bad news: it's much slower with rational coefficients, and I have no idea why:
sage: %time phi, H = algebraic_topological_model(RP3, QQ) # old version CPU times: user 1.27 s, sys: 138 ms, total: 1.41 s Wall time: 1.35 s sage: %time phi, H = AT_model(RP3, QQ) # new version CPU times: user 23.9 s, sys: 69.6 ms, total: 24 s Wall time: 24 s
Profiling the code with %prun
was not illuminating to me, and I couldn't run %crun
because I couldn't get the Google performance analysis tools to install on my machine. Optimizing code is not my strong suit, in any case.
Because of this, I haven't tried to implement cup products for Delta complexes. I think I know how to do that, but it hasn't felt worth it yet.
Changed 6 years ago by
comment:18 Changed 6 years ago by
 Commit changed from 5923e23d857ecdda88cd84d8b70d0ea2228acbde to e7f83d09ccd5aea84741886c905a541398a9405c
comment:19 Changed 6 years ago by
I think the issue comes from the fact that a category pushout is being done. This doesn't seem to happen in the finite fields of prime order cases, but it does show up for prime powers. However, for GF(4, 'a')
, it took a nontrivial amount of time (over 2 seconds on my machine).
From doing a line by line profiling, here's the lines that take the longest over QQ
:
Line # Hits Time Per Hit % Time Line Contents ============================================================== 210 182 745504 4096.2 5.8 c_bar = c  phi_old * diff * c 211 182 452404 2485.7 3.5 pi_bdry_c_bar = pi_old * diff * c_bar 236 5321 10852810 2039.6 84.1 eta_ij = (pi_old * c_j)[u_idx] 244 90 323096 3590.0 2.5 phi_old = MS_phi_t.matrix(phi_old_cols).transpose() 290 1 27459 27459.0 0.2 phi = ChainContraction(phi_data, pi, iota)
where the time is given in microseconds. Over GF(2)
, these operations are significantly faster per call.
comment:20 Changed 6 years ago by
That's helpful. The change

AT_model.py
old new 233 233 pi_cols.append(zero_vector) 234 234 for c_j_idx, c_j in enumerate(old_cells): 235 235 # eta_ij = <u, pi(c_j)>: 236 eta_ij = (pi_old * c_j)[u_idx]236 eta_ij = pi_old.row(u_idx).dot_product(c_j) 237 237 238 238 if eta_ij: 239 239 # Adjust phi(c_j).
cuts the time for AT_model(RP3, QQ)
from about 20 seconds to about 3 seconds. Still too long, but better. (At the moment, I'm getting about 7/10 of a second for the old version, just under 3 seconds with this modified new version.)
For rational matrices with lots of zero entries, it seems to be faster to multiply sparse matrices than dense ones, so I am trying to replace some of the matrices by sparse versions. I found this bug by doing this. Good times.
comment:21 Changed 6 years ago by
Another new bug: #19378.
comment:22 Changed 6 years ago by
(I like this lineprofiler, it's very useful.) A lot of time seems to be lost with (dense?) matrix operations over QQ
:
210 182 741358 4073.4 33.0 c_bar = c  phi_old * diff * c 211 182 458238 2517.8 20.4 pi_bdry_c_bar = pi_old * diff * c_bar 244 90 280498 3116.6 12.5 phi_old = MS_phi_t.matrix(phi_old_cols).transpose() 245 3402 4290 1.3 0.2 indices = [i for i in range(pi_nrows) if i not in to_be_deleted] 246 90 16370 181.9 0.7 keep = vector(base_ring, pi_nrows, {i:1 for i in indices}) 247 5411 204965 37.9 9.1 cols = [v.pairwise_product(keep) for v in pi_cols_old] 248 90 258909 2876.8 11.5 pi_old = MS_pi_t.matrix(cols).transpose()
I know we have many specialized algorithms for doing matrix manipulations over finite fields, so perhaps we are also seeing some of that here too. I'm wondering if the difference is just the number of matrix operations is just higher...(perhaps sparse matrices will work better...).
FYI  in the old implementation, this was the line taking the majority of the time
246 5321 727375 136.7 65.8 c_j_vec = vector(base_ring, old_rank, {c_j_idx: 1})
comment:23 Changed 6 years ago by
Regarding lines like c_bar = c  phi_old * diff * c
, it seems that matrixvector multiplication is faster over QQ
(compared to matrixmatrix multiplication) but slower over finite fields, so over QQ
I have changed this to c_bar = c  phi_old * (diff * c)
. I'll look at the other slow parts to see what I can do there, too.
How do you run the lineprofiler?
comment:24 Changed 6 years ago by
By the way, I now have: old timing 0.7 seconds, new timing 1.7 seconds over the rationals. Over finite fields, the new version takes about half the time (0.43 seconds compared to 0.2 seconds over GF(2)
, not quite as good an improvement when working over other prime fields).
comment:25 Changed 6 years ago by
comment:26 Changed 6 years ago by
Thanks. I'm not sure how I knew about %prun
but not %lprun
. %lprun
looks much more helpful, at least in this case.
comment:27 Changed 6 years ago by
So do you think you'll switch to the new model? It's roughly a 2x slowdown (to which I'm fairly certain it is just because you are doing more matrix multiplications), but it does offer greater flexibility. The other option would be to include both methods and choose the old one for QQ
over simplicial complexes...
comment:28 Changed 6 years ago by
My current plan is indeed to use both methods. By using your %lprun
analysis (and mine, too), I have managed to speed up both the old and new methods. Over finite fields, the old method is now about 20 times faster than it used to be: on one machine, computing algebraic_topological_model(RP3, GF(2))
used to take over 400 ms, and now takes about 20 ms, and similarly over other prime fields. Over the rationals, it used to take about 700 ms, and now takes just under 300. The new method is now faster than it used to be, but slower over all fields (about 200 ms over GF(2)
, 1500 ms over QQ
).
So the plan is to include both and use the old one for cubical and simplicial complexes, the new one only for Delta complexes. I want to figure out if I can actually implement the cup product for Delta complexes without rewriting the whole class of complexes, providing an actual class for its cells. I will try to update the branch soon in any case.
comment:29 Changed 6 years ago by
 Commit changed from e7f83d09ccd5aea84741886c905a541398a9405c to 0d2ea83c0d4a66ff254e9382376b04f90d921964
Branch pushed to git repo; I updated commit sha1. New commits:
0d2ea83  trac 6102:

comment:30 followup: ↓ 31 Changed 6 years ago by
 Milestone changed from sage6.4 to sage6.10
Those are some very good improvements.
I really don't like this:
# diff is sparse and low density. Dense matrices are faster # over finite fields, but for low density matrices, sparse # matrices are faster over the rationals. if base_ring != QQ: diff = diff.dense_matrix()
It's not a blocker for this to get a positive review, but it bugs me. Plus the extra time to convert it to a dense matrix...
I did some quick digging and there is apparently a slew of tickets on improving sparse or modn vectors/matrices: #19076 (and therein), #18231, #15104, #10312, #18312, #2705.
Was there anything in your timings to suggest a good place to go look for just using sparse matrices? Did you also test with my fixes for #19377 and #19378 (and forcing sparse matrices, or are they even necessary)?
Is there anything else you'd like to do to this before I set it to positive review?
comment:31 in reply to: ↑ 30 ; followup: ↓ 33 Changed 6 years ago by
Replying to tscrim:
Those are some very good improvements.
I really don't like this:
# diff is sparse and low density. Dense matrices are faster # over finite fields, but for low density matrices, sparse # matrices are faster over the rationals. if base_ring != QQ: diff = diff.dense_matrix()It's not a blocker for this to get a positive review, but it bugs me. Plus the extra time to convert it to a dense matrix...
On my computer, if I do
sage: from sage.homology.algebraic_topological_model import algebraic_topological_model sage: RP3 = simplicial_complexes.RealProjectiveSpace(3) sage: %timeit algebraic_topological_model(RP3, GF(2))
then without this change, it takes 104 ms per loop; with the change it takes 19.5 ms per loop. (Similar over GF(31)
, to pick a random other finite field.) So the time for converting to a dense matrix is outweighed by the speed when multiplying dense vs. sparse matrices and vectors.
I did some quick digging and there is apparently a slew of tickets on improving sparse or modn vectors/matrices: #19076 (and therein), #18231, #15104, #10312, #18312, #2705.
Was there anything in your timings to suggest a good place to go look for just using sparse matrices? Did you also test with my fixes for #19377 and #19378 (and forcing sparse matrices, or are they even necessary)?
The fixes for #19377 and #19378 won't make much of a difference, because I think the main bottlenecks are matrixmatrix multiplication and matrixvector multiplication. For #19378, it's easy enough to bypass the whole issue by testing whether the appropriate matrix is nx0
. #18231 could help, since at least with the Deltacomplex version, some of the slowest parts are constructing matrices.
I don't know where to look in the linear algebra code to improve the timings. I ran tests of the form
%timeit random_matrix(QQ, 40, density=0.1, sparse=True) * random_vector(QQ, 40, density=0.1, sparse=False)
and similarly with the second factor being a vector, and then I varied which factors were sparse. I tried with different coefficient fields, also. Over the rationals, as the density decreases, the timing for dense matrices stays pretty constant, but it speeds up for sparse matrices. (This is without even taking into account the fact that it is slower to construct random sparse matrices: see #2705.) Over finite fields, it's constant both ways, and slower for sparse matrices.
Is there anything else you'd like to do to this before I set it to positive review?
I think that cup products for Delta complexes can come on a separate ticket, if anyone ever figures it out. I'll see what I can do, but I don't want it to hold up this ticket.
comment:32 followup: ↓ 34 Changed 6 years ago by
 Branch changed from u/jhpalmieri/ATmodel to u/tscrim/ATmodel
 Commit changed from 0d2ea83c0d4a66ff254e9382376b04f90d921964 to 716469ac9519fc492467d4a635c80468880df94d
 Reviewers set to Travis Scrimshaw
I made some reviewer changes, and it's mostly tweaking docstrings and copying your sparse/dense hack to get another ~20% in the "new" version.
Ffrom taking a closer look at things, I bet we could get further speedups by not taking the transpose of the phi_old
and pi_old
matrices in the inner loops and using v * M
multiplication instead of M' * v
. I tried to do this, but I don't think I understand the interworkings of the code to get this to work (at least for the "new" version). Have you tried to do this?
Also I noticed that HomologyVectorSpaceWithBasis
represents a graded piece of the (co)homology space. Would you be opposed to me rewriting that such that it becomes the full (co)homology space/ring? I think it would simplify the overall code structure, allow easier extensions to infinite simplicial/cell complexes, and give a better interpretation of cup_product
as being the product in the cohomology ring. (Also with #18175, we could then give work towards a cap product for manifolds.)
If you would prefer one/both of these things to be pushed to later tickets, we can do that, but I'd rather get the latter done now.
New commits:
a0f20c2  Merge branch 'u/jhpalmieri/ATmodel' of trac.sagemath.org:sage into u/jhpalmieri/ATmodel

716469a  Some smaller reviewer tweaks.

comment:33 in reply to: ↑ 31 Changed 6 years ago by
Replying to jhpalmieri:
On my computer, if I do
sage: from sage.homology.algebraic_topological_model import algebraic_topological_model sage: RP3 = simplicial_complexes.RealProjectiveSpace(3) sage: %timeit algebraic_topological_model(RP3, GF(2))then without this change, it takes 104 ms per loop; with the change it takes 19.5 ms per loop. (Similar over
GF(31)
, to pick a random other finite field.) So the time for converting to a dense matrix is outweighed by the speed when multiplying dense vs. sparse matrices and vectors.
I didn't mean to imply that it wasn't a significant speedup and I apologize if I did. However that is a much larger difference than I really expected. Eeek!
The fixes for #19377 and #19378 won't make much of a difference, because I think the main bottlenecks are matrixmatrix multiplication and matrixvector multiplication. For #19378, it's easy enough to bypass the whole issue by testing whether the appropriate matrix is
nx0
. #18231 could help, since at least with the Deltacomplex version, some of the slowest parts are constructing matrices. I don't know where to look in the linear algebra code to improve the timings. I ran tests of the form%timeit random_matrix(QQ, 40, density=0.1, sparse=True) * random_vector(QQ, 40, density=0.1, sparse=False)and similarly with the second factor being a vector, and then I varied which factors were sparse. I tried with different coefficient fields, also. Over the rationals, as the density decreases, the timing for dense matrices stays pretty constant, but it speeds up for sparse matrices. (This is without even taking into account the fact that it is slower to construct random sparse matrices: see #2705.) Over finite fields, it's constant both ways, and slower for sparse matrices.
It sounds like #2705 will help for the sparse case, but I can dig around in the sparse matrix code and try to find out ways I can squeeze speed out of the matrix operations (and use hints from the tickets I cited) if you think it's worth it for this ticket. See also my previous replay
comment:34 in reply to: ↑ 32 ; followup: ↓ 35 Changed 6 years ago by
Replying to tscrim:
I made some reviewer changes, and it's mostly tweaking docstrings and copying your sparse/dense hack to get another ~20% in the "new" version.
Great.
From taking a closer look at things, I bet we could get further speedups by not taking the transpose of the
phi_old
andpi_old
matrices in the inner loops and usingv * M
multiplication instead ofM' * v
. I tried to do this, but I don't think I understand the interworkings of the code to get this to work (at least for the "new" version). Have you tried to do this?
Good idea. I just tried it and it led to no improvement, surprisingly, over the rationals, and a slowdown in characteristic 2. Maybe the lack of improvement is not that surprising, since I had already moved the slow matrix constructions out of the innermost loops, so they don't get executed as much. And maybe taking the transpose is not slow compared to the rest of matrix construction.
Also I noticed that
HomologyVectorSpaceWithBasis
represents a graded piece of the (co)homology space. Would you be opposed to me rewriting that such that it becomes the full (co)homology space/ring? I think it would simplify the overall code structure, allow easier extensions to infinite simplicial/cell complexes, and give a better interpretation ofcup_product
as being the product in the cohomology ring. (Also with #18175, we could then give work towards a cap product for manifolds.)
I think that it is natural to want both structures, the cohomology in a single degree and the cohomology in total. If you want to rewrite this part, that's okay with me. If you want to think about the most natural way to access cohomology classes, too, go ahead. I am not completely satisfied with
sage: a,b,c,d = X.cohomology_with_basis(1, QQ).gens()
Maybe
sage: H.<x> = X.cohomology_with_basis(1, QQ)
will define x0
, ..., x3
if the cohomology is 4dimensional? Or x10, ..., x13? (The problem with the anglebracket notation is that we shouldn't have to know how many generators there are ahead of time.)
I didn't mean to imply that it wasn't a significant speedup and I apologize if I did. However that is a much larger difference than I really expected. Eeek!
No need to apologize, you had a reasonable question. And it is surprising how much difference that single change makes.
comment:35 in reply to: ↑ 34 Changed 6 years ago by
Replying to jhpalmieri:
Replying to tscrim:
From taking a closer look at things, I bet we could get further speedups by not taking the transpose of the
phi_old
andpi_old
matrices in the inner loops and usingv * M
multiplication instead ofM' * v
. I tried to do this, but I don't think I understand the interworkings of the code to get this to work (at least for the "new" version). Have you tried to do this?Good idea. I just tried it and it led to no improvement, surprisingly, over the rationals, and a slowdown in characteristic 2. Maybe the lack of improvement is not that surprising, since I had already moved the slow matrix constructions out of the innermost loops, so they don't get executed as much. And maybe taking the transpose is not slow compared to the rest of matrix construction.
Yea, I confirm that there is not much time being spent on the transpose by just pulling that part out to a separate line (which I should have done beforehand, sorry). So the way to optimize this further is to speed up the matrix construction, which might depend upon the input data, and then also the dot product is the 3rd slowest line. I think we've gotten to a good point that we should just let it be for now (at least I'm not going to try and optimize it further because I will be doing the refactoring below).
Also I noticed that
HomologyVectorSpaceWithBasis
represents a graded piece of the (co)homology space. Would you be opposed to me rewriting that such that it becomes the full (co)homology space/ring? I think it would simplify the overall code structure, allow easier extensions to infinite simplicial/cell complexes, and give a better interpretation ofcup_product
as being the product in the cohomology ring. (Also with #18175, we could then give work towards a cap product for manifolds.)I think that it is natural to want both structures, the cohomology in a single degree and the cohomology in total. If you want to rewrite this part, that's okay with me.
There is a way to access the part in a single degree with the basis
function by passing in an integer:
sage: s = SymmetricFunctions(QQ).s() sage: list(s.basis(3)) [s[3], s[2, 1], s[1, 1, 1]]
This unfortunately doesn't work for most of the infinite dimensional CFM's, but there should be a generic method that works for all objects in FiniteDimensionalModulesWithBasis
. At which point, we can use the submodule
to construct the degree part (which also should have a dedicated method):
sage: s.submodule(list(s.basis(3)), already_echelonized=True) Free module generated by {0, 1, 2} over Rational Field
If you want to think about the most natural way to access cohomology classes, too, go ahead. I am not completely satisfied with
sage: a,b,c,d = X.cohomology_with_basis(1, QQ).gens()Maybe
sage: H.<x> = X.cohomology_with_basis(1, QQ)will define
x0
, ...,x3
if the cohomology is 4dimensional? Or x10, ..., x13? (The problem with the anglebracket notation is that we shouldn't have to know how many generators there are ahead of time.)
What we could do is specify variable names and then could use the inject_variables
method. I will think more about this tomorrow when I work on the above refactoring.
comment:36 Changed 6 years ago by
 Branch changed from u/tscrim/ATmodel to u/jhpalmieri/ATmodel
comment:37 Changed 6 years ago by
 Commit changed from 716469ac9519fc492467d4a635c80468880df94d to d00d31b36950f948b0be0d1d26b10543b23e3957
Turns out that cup products for Delta complexes weren't too hard to implement, so I did that.
New commits:
d00d31b  trac 6102: cup products for Delta complexes

comment:38 Changed 6 years ago by
 Commit changed from d00d31b36950f948b0be0d1d26b10543b23e3957 to 12d4cc771196f0ee301198a6ee89485a4faafb98
Branch pushed to git repo; I updated commit sha1. New commits:
12d4cc7  trac 6102: fix typo "left" > "right"

comment:39 Changed 6 years ago by
I'm still working on my refactoring, but I did #19397 for getting the degree d
components.
comment:40 Changed 6 years ago by
 Branch changed from u/jhpalmieri/ATmodel to u/tscrim/ATmodel
 Commit changed from 12d4cc771196f0ee301198a6ee89485a4faafb98 to 37517531687fffbe421b2d882e3073dcb13144e1
Done. I spent so much time trying to get the cup_product
to iterate over cohomology, but I realized that it was support to be over homology... Anyways, it works now. With the category framework, I was able to remove __pow__
(at a small cost of a not correct error for negative powers, at least for now I didn't want to muck with the AlgebrasWithBasis
code). So if you're happy with my changes, then you can set a positive review.
New commits:
8b59ed3  Making (co)homology into a graded module (algebra).

3751753  Making Sq work for inhomogeneous elements.

comment:41 Changed 6 years ago by
I will have some reviewer's changes on top of your changes soon. Meanwhile, I noticed that you removed the code related to the FiniteDimensionalAlgebra
class. I don't know much about that class, and I don't mind the removal of that code. We could also reinstate it as a method for the class CohomologyRing
("exporting" it as a FiniteDimensionalAlgebra
). Is that worth doing?
comment:42 Changed 6 years ago by
No, the CohomologyRing
class takes the place of the FiniteDimensionalAlgebra
. Was there something in that class that you were using that this version can't do? If there was, it is probably something we should generalize (on a followup ticket).
comment:43 Changed 6 years ago by
There isn't anything that I was using, but it has some methods (cardinality
, is_unitary
, is_commutative
) that I suppose some people might want.
comment:44 Changed 6 years ago by
The cardinality
should work, but it is not there and is something we should implement in generality. A default is_unitary
that returns True
could perhaps go in UnitalAlgebras
, but the cohomology ring is unital as the sum of the 0th degree components, correct (you had this in your __pow__
method too)? There should be a generic is_commutative
test for finite dimensional algebras with basis. I will open up a separate ticket when I get to my office.
comment:45 Changed 6 years ago by
This is now #19416.
comment:46 Changed 6 years ago by
 Branch changed from u/tscrim/ATmodel to u/jhpalmieri/ATmodel
comment:47 Changed 6 years ago by
 Commit changed from 37517531687fffbe421b2d882e3073dcb13144e1 to 9bfc2d2881810588de6eb1ad85870a7ac95a1b28
Okay, your turn again. If you're happy with these changes, set it to positive review. A summary of my changes:
 various documentation fixes: some docstrings didn't get changed in your refactoring, some crossreferences didn't work, etc.
 I moved several instances of
if base_ring is None
to the methods incell_complex.py
. Before, some were there but some were inalgebraic_topological_model.py
.  I removed the explicit check about immutability for simplicial complexes because it wasn't being used: once we cache the method, immutability is checked as soon as the method is called, so checking again in the method is redundant. (And if we ever decide that the method should not be cached, there is no reason to check immutability.)
comment:48 Changed 6 years ago by
 Reviewers changed from Travis Scrimshaw to Travis Scrimshaw, John Palmieri
comment:49 Changed 6 years ago by
Then it is a positive review. This is a very nice addition to Sage which I'm hoping to get some good use from (especially once #18175 and more of SageManifolds gets merged in). Thanks for all your work.
comment:50 Changed 6 years ago by
 Status changed from needs_review to positive_review
comment:51 Changed 6 years ago by
Great! Thanks very much.
comment:52 Changed 6 years ago by
 Branch changed from u/jhpalmieri/ATmodel to 9bfc2d2881810588de6eb1ad85870a7ac95a1b28
 Resolution set to fixed
 Status changed from positive_review to closed
The following code was posted by Felix Breuer on sagesupport
To use it on the Torus, for example, you can do this: