**NAME**

Grid_advanceMultiDiffusion

**SYNOPSIS**

call Grid_advanceMultiDiffusion(integer(IN) :: iVar, integer(IN) :: iSrc, integer(IN) :: iFactorA, integer(IN) :: bcTypes(6), real(IN) :: bcValues(2,6), real(IN) :: dt, real(IN) :: chi, real(IN) :: scaleFact, real(IN) :: theta, logical(IN) :: solnIsDelta, OPTIONAL,integer(IN) :: iFactorC, OPTIONAL,integer(IN) :: iFactorD OPTIONAL,integer(IN) :: pass)

**DESCRIPTION**

This routine advances a generalized diffusion problem in multiple variables of the form A*(df/dt) + C*f = div(B*grad(f)) + D , where f = f(x,t) is the Variable to be diffused (x=1D..3D position); A,B,C,D are optional given scalar factors/terms that may depend on position; they are either physcially constant in time, or at least considered time-independent for the purpose of the operation implemented here (typically by computing their values from the solution state reached by the previous time step). Presently it is used to do heat conduction and multigroup diffusion.

**ARGUMENTS**

iVar : Variable on which the diffusion operation is performed (e.g., TEMP_VAR) iFactorA :| Are factors in the equation with spatial variation. factorB :| Factor C,D are optional and are generally used iFactorC :| to represent emission/absorption in MGD. iFactorD :| iFactorA is needed only for conduction. | For this FcB variant of the interface, factorB is passed in | allocated scratch arrays, i.e., the implementation will have | to call Grid_ascGetBlkPtr to get at it. bcTypes : Presently OUTFLOW, VACUUM is supported, DIRICHLET is untested. bcValues : Values of iVar,factorB on boundary (DIRICHLET). dt : The time step. scaleFact : Factor by which the end solution is scaled (not used). chi : useful for constant diffusion problems (not used). theta : varies scheme (0-> Explicit, 1-> backward euler, 0.5 -> Crank Nicholson pass : Ignored in unsplit solver. pass=1 order of directional sweep X-Y-Z, pass=2 order of directional sweep Z-Y-X. iSrc : Ignored. solnIsDelta : Is the solution only a delta that the caller has to apply to the temperature, rather than temperature itself (ignored).

**SIDE EFFECTS**

**NOTES**

This implementation * supports: 1D, 2D, 3D Cartesian PARAMESH (with local refinement) 1D, 2D, 3D Cartesian in UG (3D untested). 1D Spherical in PARAMESH/UG 1D, 2D Cylindrical in PARAMESH/UG (R-Z) * uses HYPRE library to solve AX = B

**SEE ALSO**

Grid_dfsvCreateSystem Grid_dfsvBeginSystem Grid_dfsvAddToSystem Diffuse_solveCoupledScalar

High-Energy Density Physics

Thermonuclear-Powered Supernovae

Fluid-Structure Interaction

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The Flash Center for Computational Science is based at the University of Chicago and is supported by U.S. DOE and NSF.