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Covariant Derivative gives Error, why? (SAGE 7.5.1)

asked 2017-03-01 09:28:32 -0600

Claudia gravatar image

updated 2017-03-01 20:14:22 -0600

kcrisman gravatar image

This simple code gives an Error:

f = function('f')

B=Manifold(2,'B',start_index=1)

polar.<R,Phi> = B.chart(R'R:(0,+oo) Phi:(0,2*pi):\Phi')

G = B.riemannian_metric('G')

G[1,1]=diff(f(R),R)

G[2,2]=f(R)^2

nabla=G.connection()

S=B.tensor_field(1,1)

S[1,1]=R^(0.5)

S[2,2]=R^3

S.display()

nabla(S)

Error: TypeError: unable to convert R to an integer

This Error doesn't occur either if I avoid the square root in S[1,1]=R^(0.5), for example by writing S[1,1]=R^(0.4) or if I avoid the dependence of the derivative of f in the first entry of the metric, for example by writing G[1,1]=f(R)^2.

This Error also doesn't occur in older Sage versions, for example Sage 7.1

Thanks a lot for help!

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answered 2017-03-02 03:32:32 -0600

eric_g gravatar image

updated 2017-03-02 15:34:58 -0600

This is a known bug, related to some recent change in the treatment of derivatives of symbolic functions, cf. this discussion. In your case, the bug shows up because of both G[1,1]=diff(f(R),R) and the square root in S[1,1]=R^(0.5).

A fix is under preparation; hopefully it will be included in Sage 7.6.

EDIT: the fix is ready, cf. the comment below

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Thanks Eric, now that I know it is a bug, i will for now use an older version of Sage. Many greetings!

Claudia gravatar imageClaudia ( 2017-03-02 04:18:17 -0600 )edit

The fix is ready, as Trac ticket 22503. Without waiting for Sage 7.6, you can already use it in Sage 7.5.1 by running the following commands from your Sage root directory:

git remote add trac git://trac.sagemath.org/sage.git -t master
git pull trac public/manifolds/bug-22503
./sage -b
eric_g gravatar imageeric_g ( 2017-03-02 15:25:03 -0600 )edit

Great, I did, it works.

Claudia gravatar imageClaudia ( 2017-03-03 07:39:05 -0600 )edit

The fix is now available in the just released Sage 7.6.

eric_g gravatar imageeric_g ( 2017-03-28 07:51:15 -0600 )edit

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Asked: 2017-03-01 09:28:32 -0600

Seen: 96 times

Last updated: Mar 02