[sage-support] Re: Memory efficient calculation of the Kretschmann scalar

[Eric Gourgoulhon]

Well, if memory is really an issue, you can avoid the creation of the 
intermediate tensor fields uR and dR by writing

gc = g.components()
igc = g.inverse().components()
Rc = R.components()
kr = 0
for a in M.irange():
for b in M.irange():
for c in M.irange():
for d in M.irange():
for i in M.irange():
for j in M.irange():
for k in M.irange():
for l in M.irange():
kr += gc[[a, i]]*igc[[b, j]]*igc[[c, k]]*igc
[[d, l]] \
  *Rc[[i, b, c, d]]*Rc[[a, j, k, l]]
kr.expr()

It is certainly more efficient in term of memory, but less efficient in 
term of CPU time, since the symmetries of the Riemann tensor are not taken 
into account in the above writing.

Best wishes,

Eric.

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Re: [sage-support] Jupyter nootbook not work

[Emmanuel Charpentier]

Dear Jan;

Le dimanche 29 décembre 2019 15:26:13 UTC+1, Jan Groenewald a écrit :
>
> Hi
>
> On Sun, 29 Dec 2019 at 15:54, Szabolcs Sződi  > wrote:
> There is something simply step by step instruction for simply, ordinary 
> mortals? Couldn't find anything.
>
> In SageMath Cell type
>
> notebook()
>

Didn't wokfor me : Dagecell's interpreter complains it cant find the (pld) 
(deprecated)Sage notebook:

---ModuleNotFoundError
   Traceback (most recent call 
last) in ()> 1 notebook()
/home/sc_serv/sage/local/lib/python3.7/site-packages/sage/misc/lazy_import.pyx 
in sage.misc.lazy_import.LazyImport.__call__ 
(build/cythonized/sage/misc/lazy_import.c:3684)()351 True
352 """--> 353 return self.get_object()(*args, **kwds)354   
  355 def __repr__(self):
/home/sc_serv/sage/local/lib/python3.7/site-packages/sage/misc/lazy_import.pyx 
in sage.misc.lazy_import.LazyImport.get_object 
(build/cythonized/sage/misc/lazy_import.c:2347)()186 if 
likely(self._object is not None):187 return self._object--> 188 
return self._get_object()189 190 cpdef _get_object(self):
/home/sc_serv/sage/local/lib/python3.7/site-packages/sage/misc/lazy_import.pyx 
in sage.misc.lazy_import.LazyImport._get_object 
(build/cythonized/sage/misc/lazy_import.c:2586)()218 elif 
self._at_startup and not startup_guard:219 print('Option 
``at_startup=True`` for lazy import {0} not needed 
anymore'.format(self._name))--> 220 self._object = 
getattr(__import__(self._module, {}, {}, [self._name]), self._name)221  
   name = self._as_name222 if self._deprecation is not None:
ModuleNotFoundError: No module named 'sagenb'

 

Aren't we supposed to tell it (how ?) to use Jupyter ?

>
> Regards,
> Jan
>
>
>
> -- 
>   .~. 
>   /V\ Jan Groenewald
>  /( )\www.aims.ac.za
>  ^^-^^ 
>

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