Re: [sage-support] Re: sign problem spherical harmonics

2019-06-15 Thread Evys Ancede 
Can I someone tell me in whats files (path) are implemented de algorithm
for spherical harmonics for take a time for doing a modification in cython??

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Re: [sage-support] Sage server is not reachable

2019-06-15 Thread TAU 
On Tue, 4 Jun 2019, SUSANTA wrote:

> I have a server in which Sagemath is installed. Due to some reason my
> machine in which the server installed was shut down. After that when my all
> users search for "http://192.168.***.***:port no" for the sage server
> access, but it was not reachable. I have tried to login the server by "ssh
> -X admin@192.168.***.***" and admin password. Then I type "cd sage..." and
> then "sage". After that I type "notebook" and enter. I have opened it but it
> showing "localhost..." and my all users still cant access by
> "http://192.168.***.***:port no". What is the actual procedure to resolve
> the problem?Thanks

There might be several reasons. First check that SageMath is really 
running:

ps afx | egrep -i [s]age

then, what was the exact command for notebook()? Assuming you used port 
22334, try

fuser -n tcp 22334

or

netstat | fgrep 22334

and last, is there a hole in the firewall? Try

iptables -L | fgrep 22334

assuming you have a firewall set up.

-- 
Jori Mäntysalo

Tampereen yliopisto - Ihminen ratkaisee

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[sage-support] Re: sign problem spherical harmonics

2019-06-15 Thread Eric Gourgoulhon 
Unfortunately, the current implementation of spherical harmonics in Sage 
suffers from various issues. One is the sign convention, which is different 
from the standard one, as you pointed out. Another issue is getting false 
results for some parameters, like

sage: theta, phi = var('theta phi')
sage: spherical_harmonic(1, 1, theta, phi)
-1/4*sqrt(3)*sqrt(2)*sqrt(-sin(theta)^2)*e^(I*phi)/sqrt(pi)

The term sqrt(-sin(theta)^2) in the above expression is plain false. It 
should be sin(theta). 
This issue is related to the bug reported in
https://trac.sagemath.org/ticket/25034

As a workaround, I would recommend to use the function 
spin_weighted_spherical_harmonic with the spin weight set to zero instead 
of spherical_harmonic. The function spin_weighted_spherical_harmonic is not 
part of the main SageMath, but of the SageMath package kerrgeodesics_gw 
. So you have to install the 
later via
sage -pip install kerrgeodesic_gw

NB: on CoCalc, you have to add the option --user: 
sage -pip install --user kerrgeodesic_gw


Then, you will get (the first argument, i.e. 0, is the spin weight; if 
zero, one gets the standard spherical harmonics): 

sage: from kerrgeodesic_gw import spin_weighted_spherical_harmonic
sage: spin_weighted_spherical_harmonic(0, 2, 1, theta, phi)
-1/4*sqrt(15)*sqrt(2)*cos(theta)*e^(I*phi)*sin(theta)/sqrt(pi)
sage: spin_weighted_spherical_harmonic(0, 1, 1, theta, phi)
-1/4*sqrt(6)*e^(I*phi)*sin(theta)/sqrt(pi)


Both results agree with the standard values, as given e.g. in 
https://en.wikipedia.org/wiki/Table_of_spherical_harmonics

Eric.

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[sage-support] Re: Chromatic polynomial of a graph with loops

2019-06-15 Thread slelievre 
Tracked at

- Sage Trac ticket 27966
  set chromatic number of looped graph to zero
  https://trac.sagemath.org/ticket/27966

This should be an easy ticket.

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