[FLASH-USERS] FLASH 4-alpha release

[Anshu Dubey]

The Flash Center is pleased to announce the alpha release of the next
version of the FLASH code, version 4 alpha. FLASH 4 alpha includes
several new physics capabilities and resolves many bugs found in
previous releases up to 3.3.


Capabilities added since the FLASH3.3 release take the growth of FLASH
into two new directions simultaneously. One is a new set of physics
solver capabilities that enable the code to simulate phenomena in
High-Energy-Density Physics (HEDP). The second is inclusion of
patch-based AMR with Chombo. Much remains to be done in both these new
directions, however, they are both usable for a limited collection of
real calculations.

The HEDP capabilities are :

* Ability to model 2 temperatures and radiation in the fluid

* Diffusion and Conduction with implicit solvers

* Opacities

* Radiation transfer with multigroup diffusion

* Laser energy deposition

* Multimaterial EOS (gamma law). A tabulated version is currently
 under testing. It will soon be released as a patch. In the meantime
 it can be obtained as-is by contacting the Flash Center.

* Hybrid PIC (contributed by Mats Holmstrom). Please contact Mats
 (matsh at irf.se) for support on this section of the code.

Other new physics capabilities are :

* 3D MHD with unsplit staggered mesh implementation included
 in the release

* Super time-stepping

* Oscillation suppression in Hydro

* A new, more robust implementation of the multipole method
 for solving the Poisson equation

* Quiet start

The new infrastructural capabilities are :

* Chombo (fully functional in UG mode, AMR functional with
 restrictions)

* Mesh replication, which allows processors to be divided into
 groups where each group gets a copy of some or all of mesh variables.
 The non-replicated mesh variables are distributed among the groups
 such that each group has a unique set.

* A new, more efficient PnetCDF based I/O implementation. The implementation
 is dependent upon some feature of MPI-2, therefore does not work with
 MPI-1.

Enhancements to the existing capabilities since FLASH 3.3 are :

* Values of physical constants maintained by the PhysicalConstants
 unit have been updated to the recommended values of K. Nakamura
 et al. (Particle Data Group), J. Phys. G 37, 075021 (2010).
 Note in particular a relatively large change to the value of
 Newton's gravitational constant from 6.6725985E-8 to 6.67428E-8.
 This change could strongly affect simulations that depend on
 a balance between gravitational and other forces, and/or for which
 initial conditions where computed with a different value of the
 constant.

* Generalization of the GridParticles subunit so that it can now
 be used for moving many types of non-Eulerian data structures
 through the mesh. It is now used with PIC and Laser ray-trace in
 addition to its traditional role with Lagrangian particles.

* A longer list of changes is contained in the User's Guide in Section 1,
 What's New in This Release.



Issues that have become known since the FLASH3.3 release and have been
fixed in FLASH 4 alpha include:

* A bug was discovered in the mapping of particles to mesh which led
 to non-conservation of mass by small amounts.  The fix was
 originally distributed on the Flash mailing list as a patch for
 FLASH 3.3.

* A bug was found in the Paramesh point to point implementation of
 mapping particles to mesh.  Please see Section 1 of the FLASH
 User's Guide.


Notes / Limitations:

* Multitemperature Hydro has not been tested in 3D.

* The new multipole solver is missing the ability to treat
 a non-zero minimal radius for spherical geometries, and the
 ability to specify a point mass contribution to the potential.

* Unsplit diffusion does not work in 3D.

* HYPRE needs to be installed to use Unsplit Diffusion, Unsplit diffusion
 uses hypre-2.7.0b (might not be backward compatible).

* Usage of HYPRE Split solver in FLASH4 is only for internal debugging
purposes
 and is not generally recommended for usage.

* Split diffusion has not been tested with PARAMESH.

* Interoperability of Unsplit hydro and diffusion solver has not been
 tested extensively.

* Some configurations of hydrodynamic test problems with Chombo grid
 show worse than expected mass and total energy conservation.  Please
 see the Chombo section in Hydro chapter of the FLASH User's Guide for
 details.

* We have experienced the following abort when running
 IsentropicVortex problem with Chombo Grid:
 "MayDay: TreeIntVectSet.cpp:1995: Assertion `bxNumPts != 0' failed. !!!"
 We are currently in contact with the Chombo team to resolve this
 issue.


The release is available at:

http://flash.uchicago.edu/site/flashcode/

A stripped down version of FLASH3 that may be downloaded without a
license is also available at the same site.  This is essentially the
FLASH framework without any implementations.

The Flash Center continues to provide support for "add-ons" to the
code.

Additionally, the FLASH testing software FlashTest, which became
available with the alpha release, continues to be available for
download at:

http://flash.uchicago.edu/site/flashcode/

The code architecture and most interfaces of FLASH4 are compatible
with FLASH3.  Many, but not all parts are also backward compatible
with FLASH2.  The Flash Center has written extensive documentation
detailing how to make the transition from FLASH2 to FLASH3 as smooth
as possible.  The user should look to:

http://flash.uchicago.edu/site/flashcode/user_support/

The website also contains other documentation including a User's Guide
and a developer's section.  A new feature from FLASH3 onward is the
online description of the public interface routines to various code
units.


Development of the FLASH Code was funded by the DOE-supported
ASC/Alliance Center for Astrophysical Thermonuclear Flashes,
and continues to be funded by DOE NNSA and OASCR.  We
acknowledge support received from Lawrence Livermore National
Laboratory and the University of Chicago.

All publications resulting from the use of the FLASH Code must
acknowledge the Flash Center for Computational Science.
 Addition of the following text to the paper acknowledgments
will be sufficient.

        "The software used in this work was in part developed by the
        DOE-supported Flash Center for Computational Science
        at the University of Chicago."

--- The Flash Center, and the FLASH code team.
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