global.data Explained

Arguably the most important data file in AstroBEAR 2.0, global.data contains global domain and solver data. This data is broken up into several namelists, which are read in by different sections of the code.

GlobalData

The GlobalData namelist contains global parameters. These parameters hold for the entire problem domain, and many of them actually describe it.

• nDim: The number of dimensions in the problem. For AstroBEAR, this should be either 2 or 3, since AstroBEAR only does 2D and 3D problems. A 1D problem can be approximated with a long, narrow 2D problem domain.

• MaxLevel: The maximum refinement level for this simulation. MaxLevel is the number of refinement levels over the base grid (so a MaxLevel of 0 is fixed-grid). This value can never be less than 0, and if it is greater than 0 then the problem is an AMR problem.

• MinimumGridPoints: The minimum number of cells per dimension that a grid can have. Since a grid must have at least one cell, MinimumGridPoints should never be less than 1. A low MinimumGridPoints allows AstroBEAR to create smaller grids, which lets it refine more efficiently. Low MinimumGridPoints values also run the risk of creating a lot more grids, which will boost administrative and communication costs.

• nDomains: The number of domains comprising the problem domain. Multiple domains are useful if you want to impose different physical processes in different regions of your problem domain (i.e., different cooling curves), but most problems do not require this degree of complexity. Unless you have a specific reason for wanting multiple domains in your problem, it is best to leave this set to 1.

• lRestart: Should be set to T if you intend to restart a simulation from a Chombo file, or F if you intend to start the simulation from the beginning. You must have a Chombo file in your problem's out/ directory if you want to use this option, and it's index must match that of the RestartFrame variable (see below).

• RestartFrame: The index of the frame from which you wish to restart. This number should be greater than or equal to 0. In order to use this, you must have a Chombo file of the same index value in your problem's out/ directory (for example, RestartFrame 5 will crash unless the file out/chombo00005.hdf is present). Regardless of its value, the RestartFrame variable does nothing if the lRestart flag is set to F.

• start_time: The start time in computational units. This quantity is used to calculate the time per frame within a simulation, and should not be changed even if you are restarting the job.

• final_time: The final time (end time) in computational units. Needless to say, this should be greater than start_time.

• GmX: This is a three-integer array, with each element representing the number of cells in the domain along the given dimension. Thus, the total domain size in cells is GmX(1) * GmX(2) * GmX(3). This array is subject to the following constraints:
  • All elements must be integers.
  • All elements must be greater than or equal to MinimumGridPoints.
  • If nDim = 2, then the third GmX entry must be 1.

• GxBounds: This is a double-precision array with six values. The first three values set the lower spatial bounds of the problem domain, and the last three values set the upper bounds. For instance, the problem domain's boundaries along the x-axis are set by the first and fourth elements in GxBounds. The GxBounds array has three constraints:
  • GxBounds(1) < GxBounds(4) (i.e., they must define a legitimate x interval).
  • GxBounds(2) < GxBounds(5) (i.e., they must define a legitimate y interval).
  • IF nDim = 3, then GxBounds(3) < GxBounds(6). Otherwise, GxBounds(3) and GxBounds(6) must equal zero.
• Gmthbc: A six-integer array defining the boundary conditions along the edges of all three dimensions. If nDim = 2, then Gmthbc(3) and Gmthbc(6) should both be set to 1. The other boundary conditions can be chosen from one of the following options:
  • 1 — Extrapolated boundaries.
  • 2 — Periodic boundaries.
  • 3 — Reflecting boundaries.

• initial_maxspeed: The maximum initial wave speed; essentially, the maximum rate at which information can propagate across the grid. The higher the maximum initial wave speed, the smaller the initial timestep will be. Timesteps are adaptive in AstroBEAR, so in general it is a good idea to give yourself a higher maximum initial speed than you think you'll need—if the initial speed is too high, the system will adjust. An initial_maxspeed of about 30.d0 is common.

• iThreaded: Turns threaded execution on or off. Threading is not fully implemented in AstroBEAR 2.0, so this flag should be left at 0.

LevelData

The LevelData namelist contains values that are local to a given level. Every grid on a given level n will have the same LevelData attributes, but the values for level j != n might be substantially different.

All LevelData variables are multi-element. The data file should have values for every level from 0 to MaxLevel (see the GlobalData namelist above).

• CoarsenRatio: The refinement ratio for grids on that level. A CoarsenRatio of 2 on level n means that an i*j*k cell refined region on level n will produce a 2i*2j*2k grid on level n+1. Virtually all of our simulations use CoarsenRatios of 2. The CoarsenRatio values should always be integers.

• qTolerance: These tolerances are used within SetErrFlags() to determine whether or not to flag a cell for refinement. The higher the tolerance, the more extreme the variable gradients have to be to warrant refinement. The qTolerance variables are double-precision and must be greater than 0.d0, but a wide range of values is possible. 1.d-3 and 1.d-5 are common choices.

• DesiredFillRatios: Single or double precision values between 0 and 1. The desired fill ratio determines what fraction of the cells in a new subgrid must be flagged for refinement. If a potential subgrid's fill ratio is below its parent grid's DesiredFillRatios value, then AstroBEAR will attempt to break it into smaller grids with higher fill ratios. Problems with low fill ratios will refine more cells than they need to, but will likely use fewer grids to do so. It becomes a trade-off between the cost of additional refinement and the cost of grid management and communication. Typical fill ratios range between .5 to .99 (although .99 can be extremely slow).

IOData

DomainData

PoissonData