Re: [sage-support] Viewers in cocalc?

2019-02-27 Thread Dima Pasechnik
On Mon, Feb 25, 2019 at 11:26 PM david.guichard wrote: > > When I try to specify a viewer in a plot3d I get an error if I try anything > other than "tachyon". Even viewer='threejs' throws an error, though I think > the default viewer is threejs. What I'm really looking for is a viewer that > le

Re: [sage-support] about the speed of tha Magma interface

2019-02-27 Thread Dima Pasechnik
On Tue, Feb 26, 2019 at 8:32 PM Pierre Guillot wrote: > > > >Can Sage do this determinant on its own? > > Sage tries to convert the matrix to a dense one before computing the > determinant (the documentation for sparse matrices says so). And as a result, > you never see the end of it, no. > I pr

[sage-support] surface normal vector of polyhedron face

2019-02-27 Thread Daniel Krenn
Say we have sage: P = polytopes.simplex(2) sage: P.faces(1) (<0,1>, <0,2>, <1,2>) Is there an easy way in SageMath to compute the in- or outward surface normal vector of these faces of P? (in contrast to doing it all from scratch). If not, are there methods that might help, so that not everything

Re: [sage-support] about the speed of tha Magma interface

2019-02-27 Thread Pierre Guillot
> I presume your polynomial entries are mostly constants, otherwise > you'd get a really huge polynomial as an answer. Do you know if your > matrix has many rows/columns with just one non-0? This could be a good > heuristic to do for sparse determinants, get rid of these first of > all... all the

Re: [sage-support] surface normal vector of polyhedron face

2019-02-27 Thread Dima Pasechnik
On Wed, Feb 27, 2019 at 1:02 PM Daniel Krenn wrote: > > Say we have > > sage: P = polytopes.simplex(2) > sage: P.faces(1) > (<0,1>, <0,2>, <1,2>) > > Is there an easy way in SageMath to compute the in- or outward surface > normal vector of these faces of P? (in contrast to doing it all from > scra

Re: [sage-support] surface normal vector of polyhedron face

2019-02-27 Thread Daniel Krenn
On 27.02.19 14:34, Dima Pasechnik wrote: > On Wed, Feb 27, 2019 at 1:02 PM Daniel Krenn wrote: >> Is there an easy way in SageMath to compute the in- or outward surface >> normal vector of these faces of P? (in contrast to doing it all from >> scratch). If not, are there methods that might help, s

Re: [sage-support] surface normal vector of polyhedron face

2019-02-27 Thread Dima Pasechnik
On Wed, Feb 27, 2019 at 1:52 PM Daniel Krenn wrote: > > On 27.02.19 14:34, Dima Pasechnik wrote: > > On Wed, Feb 27, 2019 at 1:02 PM Daniel Krenn wrote: > >> Is there an easy way in SageMath to compute the in- or outward surface > >> normal vector of these faces of P? (in contrast to doing it all

Re: [sage-support] surface normal vector of polyhedron face

2019-02-27 Thread 'luisfe' via sage-support
On Wednesday, February 27, 2019 at 2:52:36 PM UTC+1, Daniel Krenn wrote: > > I suppose in non-full-dimensional case you still can use > > P.inequalities() as above, > > projecting them on the affine hull of P. > > Yes, this is the interesting case. The problem then is going back from > the p

Re: [sage-support] surface normal vector of polyhedron face

2019-02-27 Thread Daniel Krenn
On 27.02.19 15:35, Dima Pasechnik wrote: >> Yes, this is the interesting case. The problem then is going back from >> the projection. I guess that orthogonality is ususally destroyed here... > One can ensure it is orthonormal: > > sage: P = polytopes.simplex(2) > sage: > M=P.affine_hull(orthonorm

Re: [sage-support] surface normal vector of polyhedron face

2019-02-27 Thread Daniel Krenn
On 27.02.19 16:12, Daniel Krenn wrote: > On 27.02.19 15:35, Dima Pasechnik wrote: >> So you get your normal vectors in the subspace parallel to the affine hull >> of P. > > Thank you, looks easy :) (I am now just using orthogonal=True in my > case, as I do not want to get non-rational.) FYI, ort