**NAME**

Diffuse_solveScalar

**SYNOPSIS**

call Diffuse_solveScalar (integer, intent(IN) :: iVar, integer, intent(IN) :: iFactorB, integer, intent(IN) :: iFactorA, integer, intent(IN) :: bcTypes(6), real, intent(IN) :: bcValues(2,6), real, intent(IN) :: dt, real, intent(IN) :: scaleFact, real, intent(IN) :: chi, real, intent(IN) :: theta, integer, OPTIONAL, intent(IN) :: pass, integer, intent(IN) :: blockCount, integer,dimension(blockCount),intent(IN) :: blockList, integer, intent(IN), OPTIONAL :: iFactorC, integer, intent(IN), OPTIONAL :: iFactorD)

**DESCRIPTION**

This routine advances a generalized diffusion operator 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 operatorion is performed (e.g TEMP_VAR) iFactorA :| Are factors in the equation with spatial variation. iFactorB :| Factor C,D are optional and are generally used iFactorC :| to represent emission/absorption in MGD. iFactorD :| iFactorA is needed only for conduction. bcTypes : Presently OUTFLOW, VACUUM is supported, DIRICHLET is untested. bcValues : Values of iVar,iFactorB 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. blockCount : The number of blocks in the list. blockList : The list of blocks on which the solution must be updated.

**SIDE EFFECTS**

**NOTES**

Stub implementation.

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