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Code Saturne version 1.3.2 practical user’s
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IPOL is necessarily null with the Jacobi algorithm.
Concerning the computational time, the performance depends on the case. If a preconditioning method different from the diagonal preconditioning is to be used, it seems to
be better to restrict to a first-order preconditioning (IPOL=1). This preconditioning
may save up to 10% of time in some cases but in the others it may also increase the
computational time by a few percents
always useful
NITMAX
IA
integer > 0
[10000]
O
L3
for each unknown IVAR, maximum number of iterations for the solution of the linear
systems: NITMAX(IVAR)
when the algebraic multigrid option is activated for the variable IVAR (IMGR(IVAR)=1),
NITMAX(IVAR) is the maximum number of iterations for the solution on the coarsest
mesh
always useful
EPSILO
RA
real number > 0
[1.D-8,1.D-5]
O
L3
for each unknown IVAR, relative precision for the solution of the linear system. The
default value is EPSILO(IVAR)=1.D-8. This value is set low on purpose. When there
are enough iterations on the reconstruction of the right-hand side of the equation, the
value may be increased (by default, in case of second-order in time, with NSWRSM
= 5 or 10, EPSILO is increased to 1.D-5).
always useful
IMGR
IA
0 or 1
[0]
O
L3
for each unknown IVAR, indicates the use (IMGR(IVAR)=1) or not (=0) of the algebraic multigrid method for the solution of the linear systems
IMGR(IVAR) can be set independently for every variable
always useful. Generally, its use is designed for the variable “pressure” in case of
meshes with strongly stretched cells. It is recommended not to modify IMGR
NCEGRM
I
integer > 0
[30]
O
for the multigrid method, maximum number of cells on the coarsest grid
useful if and only if IMGR(IVAR) = 1 for at least one variable IVAR
NCYMAX
IA
integer > 0
[100]
O
L3
for each unknown IVAR, NCYMAX(IVAR) is the maximum number of cycles when
using the multigrid method.
useful if and only if IMGR(IVAR) = 1
NGRMAX
I
16 integer 6NGRMMX
[NGRMMX]
when using the multigrid method, maximum number of grid levels
useful if and only if IMGR(IVAR) = 1 for at least one variable IVAR
NITMGF
IA
integer > 0
[10]
O
L3
for each unknown IVAR, NITMGF(IVAR) is the maximum number of iterations on
the intermediary grids when the multigrid method is used
useful if and only if IMGR(IVAR) = 1
O
L3
L3
Warning
The algebraic multigrid method does not work when the mesh contains subdivided faces (or more
generally when two different faces have the same pair of neighbors). In addition, it has been validated up
to now only for the variable “pressure” (IMGR(IPR(IPHAS))=1) and with non-parallel computations.