Open ritzvik opened 4 years ago
@spino17 Can you help in any way ?
That’s a collection of issues, each requiring deep theoretical knowledge. I wouldn’t recommend that you take these up. Good first issues, maybe??
Regards, Ritwik
On 02-Feb-2020, at 3:06 PM, sagnik-chatterjee notifications@github.com wrote:
Can i take up this issue ?
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Hi, I know how "lorentz transformation" of Christoffel symbols should work, since they are not actual tensors. However, I am new to this project, so would be happy if someone wants to work together on it, I can provide some references and formula for that.
Hi, I know how "lorentz transformation" of Christoffel symbols should work, since they are not actual tensors. However, I am new to this project, so would be happy if someone wants to work together on it, I can provide some references and formula for that.
I would love to collaborate, let's get things done with #427 first. BTW, it would be great help!
@gimseng However, I am thinking of deprecating lorentz transform and implementing change of basis vectors, lorentz transform being a special case of the latter.
What do you say?
Sure, I think doing a general coordinate transformation (or you call it basis change) is more relevant and useful for a GR package. I could start working on this. However, I wanted to do it probably with git and stuff so maybe it will be a little slower, and I will ask lots of questions to make sure I don't screw with master and I want to do rebase and squashing properly. If its ok with you all, I will go dig around to figure out how and what should be done.
On another note, I think for Lorentz transformation, the Christoffel will transform like appropriate Lorentz tensors, since the "extra terms" vanish for Lorentz-transfomation. So they are Lorentz tensors but not general-covariant tensors. If need be, and if some points me towards the right place, I could write a few lines to explain this in a doc or issue ticket or something.
Finally, what is this issue with "parent metric"? Is this a class inheritance thing or some GR thing?
Okay then! Have a look at the symbolic module. There are many examples on their usage. Let’s start with general coordinate transform then. With this we won’t have the luxury of ignoring extra terms for pseudo-tensors. Also we need to devise a strategy on how to implement them!
Regards, Ritwik
On 12-Feb-2020, at 1:21 PM, Gim Seng notifications@github.com wrote:
Sure, I think doing a general coordinate transformation (or you call it basis change) is more relevant and useful for a GR package. I could start working on this. However, I wanted to do it probably with git and stuff so maybe it will be a little slower, and I will ask lots of questions to make sure I don't screw with master and I want to do rebase and squashing properly. If its ok with you all, I will go dig around to figure out how and what should be done.
On another note, I think for Lorentz transformation, the Christoffel will transform like appropriate Lorentz tensors, since the "extra terms" vanish for Lorentz-transfomation. So they are Lorentz tensors but not general-covariant tensors. If need be, and if some points me towards the right place, I could write a few lines to explain this in a doc or issue ticket or something.
Finally, what is this issue with "parent metric"? Is this a class inheritance thing or some GR thing?
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See from_metric
classmethod in ChristoffelSymbols
, you would understand what parent_metric
is about. It actually preserves the metric from which other quantities are derived.
I see, if I understood correctly, the structure of implementations are such that you do something.from_somethingelse(...) to actually calculation, say Christoffel / Riemann / Ricci from the appropriate object (say metric/Christoffel/Riemann).
So the Christoffel method has a from_metric method, which computes the Christoffel symbol, and return as a tensor class.
If I understood the issue correctly, now under Lorentz/general coordinate transformations, do we want to keep track of which metric a Christoffel symbol was constructed from? If we did, when we applied a transformation/basis change to the Christoffel symbol, returning the Christoffel symbol in a new coordinate/basis, the question/issue is then: do we transform the original metric (in original coordinates/basis) to the metric in new coordinate and assigning this to be the parent metric of the Christoffel symbol in new coordinate?
@gimseng Yes, you understood this right. Along with transformation of the derived quantity, we also need to transform the metric from which it is derived, and set the new metric as parent_metric
.
But we would need to decide on whether to drop lorentz altogether in favor of general transformation. I say yes! If it is yes from your side also, we can first work on general transformation, and later drop lorentz, saving us the efforts here!
And this parent_metric
thing would also apply in general transformations. There's no running from this problem :(
Also, here is a link detailing mathematics behind transformation of christoffels
hi I am a little busy these two weeks, maybe I will check in again after I finished my busy weeks?
Sure ! Open source is people coming together to contribute at their own convenience.
Regards, Ritwik
On 14-Feb-2020, at 2:24 PM, Gim Seng notifications@github.com wrote:
hi I am a little busy these two weeks, maybe I will check in again after I finished my busy weeks?
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I think, it is better to have mathematical operations as mixins that suitable objects can then derive from. Perhaps one can look into this.
Also ref: https://github.com/einsteinpy/einsteinpy/issues/497#issuecomment-1295053256.
🐞 Problem There is a lot to be desired regarding
lorentz_transform
function in the classes ofsymbolic
module. This issue consolidates a number of problems into a single issue.🎯 Goal
lorentz_transform
across all the classes and implement them.lorentz_transform
implemented inChristoffelSymbols
is probably incorrect, Christoffel Symbols being a pseudo-tensor. Research about this, and change the implementation along with suitable tests.💡 Possible solutions
📋 Steps to solve the problem
Addresses #<put issue number here>