[ODE] Faster ODE
Henri Hakl
henri at cs.sun.ac.za
Thu Nov 21 02:48:02 2002
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Hi ODE :)
Please can somebody look at this and experiment with the file?
LDLT decomposition is one of the primary computational activities in =
ODE's physics engine. LDLT =3D Lower Diagonal Lower Transposed, meaning =
a constraint matrix A (that describes the physics of a world) can be =
decomposed into two matrices (L and D, where L is a lower triangular =
matrix (all entries above the diagonal are zero) and D is a diagonal =
matrix (all entries except the diagonal are zero)). Now A =3D L D L' =
(A equals the lower matrix times the diagonal matrix times the =
transposed lower matrix.) The A matrix varies in size and is typically =
between 10x10 and 500x500 for ODE (depending on
how many constraints/collisions/etc need to be solved for a given =
simulation step).
This LDLT decomposition needs to be solved with every step and is quite =
computationally intensive. I've looked at the stldlt.c file that is part =
of the ODE source and it looks to me like it could be improved upon. =
Unforetunately I use Delphi, so I cannot test my suggested modifications =
directly (though the Delphi version seems fine and considerably faster =
then the original).
The file http://www.cs.sun.ac.za/~henri/fastldlt_henri.c is a =
replacement for fastldlt.c and should (barring errors) work flawlessly =
and faster then the original.
Let me know if it works, thanks :)
Henri
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<DIV>Hi ODE :)</DIV>
<DIV> </DIV>
<DIV>Please can somebody look at this and experiment with the =
file?</DIV>
<DIV> </DIV>
<DIV>LDLT decomposition is one of the primary computational activities =
in ODE's=20
physics engine. LDLT =3D Lower Diagonal Lower Transposed, meaning a =
constraint=20
matrix A (that describes the physics of a world) can be decomposed into =
two=20
matrices (L and D, where L is a lower triangular matrix (all entries =
above the=20
diagonal are zero) and D is a diagonal matrix (all entries except =
the=20
diagonal are zero)). Now A =3D L D L' (A equals the lower =
matrix times=20
the diagonal matrix times the transposed lower matrix.) The A matrix =
varies in=20
size and is typically between 10x10 and 500x500 for ODE (depending =
on<BR>how=20
many constraints/collisions/etc need to be solved for a given simulation =
step).<BR><BR>This LDLT decomposition needs to be solved with every step =
and is=20
quite computationally intensive. I've looked at the stldlt.c file that =
is part=20
of the ODE source and it looks to me like it could be improved upon.=20
Unforetunately I use Delphi, so I cannot test my=20
suggested modifications directly (though the Delphi version =
seems fine=20
and considerably faster then the original).<BR><BR>The file <A=20
href=3D"http://www.cs.sun.ac.za/~henri/fastldlt_henri.c">http://www.cs.su=
n.ac.za/~henri/fastldlt_henri.c</A>=20
is a replacement for fastldlt.c and should (barring errors) work =
flawlessly and=20
faster then the original.</DIV>
<DIV> </DIV>
<DIV>Let me know if it works, thanks :)</DIV>
<DIV> Henri</DIV>
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