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metric to christoffel symbols yielding overflow

asked 2020-09-23 21:56:09 +0200

drwbia gravatar image

updated 2020-09-24 02:45:39 +0200

slelievre gravatar image

In a Sage 9.1 Jupyter notebook I tried the following SageManifolds commands

M = Manifold(4, 'M', structure='Lorentzian')

Mani.<t,X,rh,ph> = M.chart(r"t X:(-oo,+oo) rh:(0,+oo):\rho ph:(0,2*pi):\phi")

B = function('B')(X,rh,ph)
d_Ph_X = function('d_Ph_X')(X,rh,ph)
d_Ph_rh = function('d_Ph_rh')(X,rh,ph)
d_Ph_ph = function('d_Ph_ph')(X,rh,ph)

g = M.metric()

g[0,0] = (-1+B**2*  ((d_Ph_X/B**2)**2 +(d_Ph_rh/B**2)**2 +((1/rh*d_Ph_ph/B**2)**2     )))

g[1,1] = B**2
g[2,2] = B**2
g[3,3] = rh**2*B**2

g[0,1] = B**2*(d_Ph_X/B**2)
g[0,2] = B**2*( d_Ph_rh/B**2)
g[0,3] = B**2*( d_Ph_ph/B**2)


The last line makes the notebook overflow... i really don't understand why.

the computation, even if it is rather tedious, seems straightforward to me...

Any idea? Any help would be greatly appreciated.

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answered 2020-09-24 11:25:59 +0200

eric_g gravatar image

You should simplify $g_{00}$ in the input, via

g[0,0] = (-1+B**2*  ((d_Ph_X/B**2)**2 +(d_Ph_rh/B**2)**2 +((1/rh*d_Ph_ph/B**2)**2     ))).simplify_full()

Then it works: the Christoffel symbols are displayed in 2 min on my computer.

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thx a lot for your time/insight! actually it did not work on my computer with sage 9.1 and it did work on the 1st attempt with sage 8.9, something really is different with 9.1 i guess... by the way using sage 8.9 also enabled me to retrieve all my .sws which were completely impossible to load on sage 9.1... life is strange sometimes ;) --> i now am a happy sage 8.9 user

drwbia gravatar imagedrwbia ( 2020-09-25 19:54:26 +0200 )edit

For me, it works well with Sage 9.1. Maybe something is weird with your Sage 9.1 install? How did you install it?

eric_g gravatar imageeric_g ( 2020-09-25 21:41:05 +0200 )edit

Regarding the .sws issue: you should take the opportunity of having a running Sage 8.9 to convert all your *.sws files to *.ipynb (Jupyter format). See this post.

eric_g gravatar imageeric_g ( 2020-09-25 21:45:39 +0200 )edit

@eric_g --> I installed it via conda

conda install mamba -c conda-forge # installs mamba

mamba create -n sage sage -c conda-forge # replaces "conda create..."

indeed you're right about the converting process that i should follow, thx I just found out that doing what you said indeed enabled the computation on my computer. without any modification of the memory available for sage. However a rather small modification of this metric does not work even with simplify_full, whereas it does with sage 8.9 (yielding "unreasonably" long expressions ^^)

drwbia gravatar imagedrwbia ( 2020-09-26 18:22:41 +0200 )edit

B = function('B')(X,rh)

d_Ph_X = function('d_Ph_X')(X,rh,ph)

d_Ph_rh = function('d_Ph_rh')(X,rh,ph)

d_Ph_ph = function('d_Ph_ph')(X,rh,ph)

P = function('P')(t)

g = M.metric()

g[0,0] = (-1+B2* ((P+d_Ph_X/B2)2 +(d_Ph_rh/B2)2 +((1/rhd_Ph_ph/B2)*2 ))).simplify_full()

g[1,1] = (B**2).simplify_full()

g[2,2] = (B**2).simplify_full()

g[3,3] = (rh2*B2).simplify_full()

g[0,1] = (B2*(P+d_Ph_X/B2)).simplify_full()

g[0,2] = (B2*( d_Ph_rh/B2)).simplify_full

g[0,2] = (B2*( d_Ph_rh/B2)).simplify_full()

g[0,3] = (B2*( d_Ph_ph/B2)).simplify_full()



drwbia gravatar imagedrwbia ( 2020-09-26 20:05:34 +0200 )edit

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Asked: 2020-09-23 21:56:09 +0200

Seen: 340 times

Last updated: Sep 24 '20