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config["Solver"]

"Solver":
{
    "Order": <int>,
    "PartialAssemblyOrder": <int>,
    "Device": <string>,
    "Backend": <string>,
    "Eigenmode":
    {
        ...
    },
    "Driven":
    {
        ...
    },
    "Transient":
    {
        ...
    },
    "Electrostatic":
    {
        ...
    },
    "Magnetostatic":
    {
        ...
    },
    "Linear":
    {
        ...
    }
}

with

"Order" [1] : Finite element order (degree). Arbitrary high-order spaces are supported.

"PartialAssemblyOrder" [1] : Order at which to switch from full assembly of finite element operators to partial assembly. Setting this parameter equal to 1 will fully activate operator partial assembly on all levels, while setting it to some large number (greater than the finite element order) will result in fully assembled operators as sparse matrices.

"Device" ["CPU"] : The runtime device configuration passed to MFEM in order to activate different options specified during configuration. The available options are:

  • "CPU"
  • "GPU"
  • "Debug"

The "GPU" option will automatically activate the cuda or hip device based on whether MFEM is built with CUDA (MFEM_USE_CUDA=ON) or HIP (MFEM_USE_HIP=ON) support. When Palace is built with OpenMP support (PALACE_WITH_OPENMP=ON), omp is automatically added to the list of activated MFEM devices. The "Debug" option for MFEM's debug device is useful for debugging issues associated with GPU-based runs of Palace.

"Backend" [""] : Specifies the libCEED backend to use for the simulation. If no backend is specified, a suitable default backend is selected based on the given config["Solver"]["Device"].

"Eigenmode" : Top-level object for configuring the eigenvalue solver for the eigenmode simulation type. Thus, this object is only relevant for config["Problem"]["Type"]: "Eigenmode".

"Driven" : Top-level object for configuring the frequency domain driven simulation type. Thus, this object is only relevant for config["Problem"]["Type"]: "Driven".

"Transient" : Top-level object for configuring the time domain driven simulation type. Thus, this object is only relevant for config["Problem"]["Type"]: "Transient".

"Electrostatic" : Top-level object for configuring the electrostatic simulation type. Thus, this object is only relevant for config["Problem"]["Type"]: "Electrostatic".

"Magnetostatic" : Top-level object for configuring the magnetostatic simulation type. Thus, this object is only relevant for config["Problem"]["Type"]: "Magnetostatic".

"Linear" : Top-level object for configuring the linear solver employed by all simulation types.

Advanced solver options

  • "QuadratureOrderJacobian" [false]
  • "ExtraQuadratureOrder" [0]

solver["Eigenmode"]

"Eigenmode":
{
    "Target": <float>,
    "Tol": <float>,
    "MaxIts": <int>,
    "MaxSize": <int>,
    "N": <int>,
    "Save": <int>,
    "Type": <int>,
    "ContourTargetUpper": <float>,
    "ContourAspectRatio": <float>,
    "ContourNPoints": <int>
}

with

"Target" [None] : (Nonzero) frequency target above which to search for eigenvalues, GHz.

"Tol" [1.0e-6] : Relative convergence tolerance for the eigenvalue solver.

"MaxIts" [0] : Maximum number of iterations for the iterative eigenvalue solver. A value less than 1 uses the solver default.

"MaxSize" [0] : Maximum subspace dimension for eigenvalue solver. A value less than 1 uses the solver default.

"N" [1] : Number of eigenvalues to compute.

"Save" [0] : Number of computed field modes to save to disk for visualization with ParaView. Files are saved in the paraview/ directory under the directory specified by config["Problem"]["Output"].

"Type" ["Default"] : Specifies the eigenvalue solver to be used in computing the given number of eigenmodes of the problem. The available options are:

  • "SLEPc"
  • "ARPACK"
  • "Default" : Use the default eigensolver. Currently, this is the Krylov-Schur eigenvalue solver from "SLEPc".

Advanced eigenmode solver options

  • "PEPLinear" [true]
  • "Scaling" [true]
  • "StartVector" [true]
  • "StartVectorConstant" [false]
  • "MassOrthogonal" [false]

solver["Driven"]

"Driven":
{
    "MinFreq": <float>,
    "MaxFreq": <float>,
    "FreqStep": <float>,
    "SaveStep": <int>,
    "Restart": <int>,
    "AdaptiveTol": <float>,
    "AdaptiveMaxSamples": <int>,
    "AdaptiveConvergenceMemory": <int>
}

with

"MinFreq" [None] : Lower bound of frequency sweep interval, GHz.

"MaxFreq" [None] : Upper bound of frequency sweep interval, GHz.

"FreqStep" [None] : Frequency step size for frequency sweep, GHz.

"SaveStep" [0] : Controls how often, in number of frequency steps, to save computed fields to disk for visualization with ParaView. Files are saved in the paraview/ directory under the directory specified by config["Problem"]["Output"].

"Restart" [1] : Iteration (1-based) from which to restart for a partial frequency sweep simulation. That is, the initial frequency will be computed as "MinFreq" + ("Restart" - 1) * "FreqStep".

"AdaptiveTol" [0.0] : Relative error convergence tolerance for adaptive frequency sweep. If zero, adaptive frequency sweep is disabled and the full-order model is solved at each frequency step in the specified interval. If positive, this tolerance is used to ensure the reliability of the reduced-order model relative to the full-order one in the frequency band of interest.

"AdaptiveMaxSamples" [20] : Maximum number of frequency samples used to construct the reduced-order model for adaptive fast frequency sweep, if the specified tolerance ("AdaptiveTol") is not met first.

"AdaptiveConvergenceMemory" [2] : Memory used for assessing convergence of the adaptive sampling algorithm for constructing the reduced-order model for adaptive fast frequency sweep. For example, a memory of "2" requires two consecutive samples which satisfy the error tolerance.

solver["Transient"]

"Transient":
{
    "Type": <string>,
    "Excitation": <string>,
    "ExcitationFreq": <float>,
    "ExcitationWidth": <float>,
    "MaxTime": <float>,
    "TimeStep": <float>,
    "SaveStep": <int>
}

with

"Type" ["Default"] : Specifies the time integration scheme used for the discretization of the second-order system of differential equations. The available options are:

  • "GeneralizedAlpha" : The second-order implicit generalized-$\alpha$ method with $\rho_\inf = 1.0$. This scheme is unconditionally stable.
  • "NewmarkBeta" : The second-order implicit Newmark-$\beta$ method with $\beta = 1/4$ and $\gamma = 1/2$. This scheme is unconditionally stable.
  • "CentralDifference" : The second-order explicit central difference method, obtained by setting $\beta = 0$ and $\gamma = 1/2$ in the Newmark-$\beta$ method. In this case, the maximum eigenvalue of the system operator is estimated at the start of the simulation and used to restrict the simulation time step to below the maximum stability time step.
  • "Default" : Use the default "GeneralizedAlpha" time integration scheme.

"Excitation" [None] : Controls the time dependence of the source excitation. The available options are:

  • "Sinusoidal" : A sinusoidal excitation at a user specified frequency.
  • "Gaussian" : A Gaussian pulse with a user specified width which defines the bandwidth.
  • "DifferentiatedGaussian" : A differentiated Gaussian pulse with a user specified width which defines the bandwidth.
  • "ModulatedGaussian" : A modulated Gaussian pulse at a user specified center frequency and width used to excite the system without any DC component.
  • "Ramp" : A differentiable unit step function to model the ramp up to a DC signal.
  • "SmoothStep" : A smoother many-times differentiable unit step function to model the ramp up to a DC signal over a specified width of time.

"ExcitationFreq" [None] : Center frequency used for harmonic source excitations, GHz. Only relevant when "Excitation" is one of "Sinusoidal", "Gaussian", "DifferentiatedGaussian", or "ModulatedGaussian".

"ExcitationWidth" [None] : Pulse width for Gaussian-type source excitations, ns. Only relevant when "Excitation" is one of "Gaussian", "DifferentiatedGaussian", "ModulatedGaussian", or "SmoothStep".

"MaxTime" [None] : End of simulation time interval, ns. Transient simulations always start from rest at $t = 0.0$.

"TimeStep" [None] : Uniform time step size for time integration, ns.

"SaveStep" [0] : Controls how often, in number of time steps, to save computed fields to disk for visualization with ParaView. Files are saved in the paraview/ directory under the directory specified by config["Problem"]["Output"].

solver["Electrostatic"]

"Electrostatic":
{
    "Save": <int>
}

with

"Save" [0] : Number of computed electric field solutions to save to disk for visualization with ParaView, ordered by the entries in the computed capacitance matrix. Files are saved in the paraview/ directory under the directory specified by config["Problem"]["Output"].

solver["Magnetostatic"]

"Magnetostatic":
{
    "Save": <int>
}

with

"Save" [0] : Number of computed magnetic field solutions to save to disk for visualization with ParaView), ordered by the entries in the computed inductance matrix. Files are saved in the paraview/ directory under the directory specified by config["Problem"]["Output"].

solver["Linear"]

"Linear":
{
    "Type": <string>,
    "KSPType": <string>,
    "Tol": <float>,
    "MaxIts": <int>,
    "MaxSize": <int>,
    "MGMaxLevels": <int>,
    "MGCoarsenType": <string>,
    "MGCycleIts": <int>,
    "MGSmoothIts": <int>,
    "MGSmoothOrder": <int>,
    "PCMatReal": <bool>,
    "PCMatShifted": <bool>,
    "PCSide": <string>,
    "DivFreeTol": <float>,
    "DivFreeMaxIts": <float>,
    "EstimatorTol": <float>,
    "EstimatorMaxIts": <float>,
    "EstimatorMG": <bool>,
    "GSOrthogonalization": <string>
}

with

"Type" ["Default"] : Specifies the solver used for preconditioning the linear system of equations to be solved for each simulation type. The available options are:

  • "SuperLU" : The SuperLU_DIST sparse direct solver in real double precision is used to factorize the system matrix. For frequency domain problems this uses a real approximation to the true complex linear system matrix. This option is only available when Palace has been built with SuperLU_DIST support.
  • "STRUMPACK" : The STRUMPACK sparse direct solver in real double precision is used to factorize the system matrix. For frequency domain problems this uses a real approximation to the true complex linear system matrix. This option is only available when Palace has been built with STRUMPACK support.
  • "MUMPS" : The MUMPS sparse direct solver in real double precision is used to factorize the system matrix. For frequency domain problems this uses a real approximation to the true complex linear system matrix. This option is only available when Palace has been built with MUMPS support.
  • "AMS" : Hypre's Auxiliary-space Maxwell Solver (AMS), an algebraic multigrid (AMG)-based preconditioner.
  • "BoomerAMG" : The BoomerAMG AMG solver from Hypre.
  • "Jacobi" : Diagonal scaling with a simple Jacobi preconditioner (not recommended in general).
  • "Default" : Use the default "AMS" solver for simulation types involving definite or semi-definite curl-curl operators (time domain problems as well as magnetostatics). For frequency domain problems, use a sparse direct solver if available, otherwise uses "AMS". For electrostatic problems, uses "BoomerAMG".

"KSPType" ["Default"] : Specifies the iterative Krylov subspace solver type for solving linear systems of equations arising for each simulation type. The available options are:

  • "CG"
  • "GMRES"
  • "FGMRES"
  • "Default" : Use the default "GMRES" Krylov subspace solver for frequency domain problems, that is when config["Problem"]["Type"] is "Eigenmode" or "Driven". For the other simulation types, the linear system matrix is always real and symmetric positive definite (SPD) and the preconditioned conjugate gradient method ("CG") is used as the Krylov solver.

"Tol" [1.0e-6] : Relative residual convergence tolerance for the iterative linear solver.

"MaxIts" [100] : Maximum number of iterations for the iterative linear solver.

"MaxSize" [0] : Maximum Krylov space size for the GMRES and FGMRES solvers. A value less than 1 defaults to the value specified by "MaxIts".

"MGMaxLevels" [100] : Chose whether to enable geometric multigrid preconditioning which uses p- and h-multigrid coarsening as available to construct the multigrid hierarchy. The solver specified by "Type" is used on the coarsest level. Relaxation on the fine levels is performed with Chebyshev smoothing.

"MGCoarsenType" ["Logarithmic"] : Coarsening to create p-multigrid levels.

  • "Logarithmic"
  • "Linear"

"MGCycleIts" [1] : Number of V-cycle iterations per preconditioner application for multigrid preconditioners (when "UseMultigrid" is true or "Type" is "AMS" or "BoomerAMG").

"MGSmoothIts" [1] : Number of pre- and post-smooth iterations used for multigrid preconditioners (when "UseMultigrid" is true or "Type" is "AMS" or "BoomerAMG").

"MGSmoothOrder" [0] : Order of polynomial smoothing for geometric multigrid preconditioning (when "UseMultigrid" is true). A value less than 1 defaults to twice the solution order given in config["Solver"]["Order"] or 4, whichever is larger.

"PCMatReal" [false] : When set to true, constructs the preconditioner for frequency domain problems using a real-valued approximation of the system matrix. This is always performed for the coarsest multigrid level regardless of the setting of "PCMatReal".

"PCMatShifted" [false] : When set to true, constructs the preconditioner for frequency domain problems using a positive definite approximation of the system matrix by flipping the sign for the mass matrix contribution, which can help performance at high frequencies (relative to the lowest nonzero eigenfrequencies of the model).

"PCSide" ["Default"] : Side for preconditioning. Not all options are available for all iterative solver choices, and the default choice depends on the iterative solver used.

  • "Left"
  • "Right"
  • "Default"

"DivFreeTol" [1.0e-12] : Relative tolerance for divergence-free cleaning used in the eigenmode simulation type.

"DivFreeMaxIts" [1000] : Maximum number of iterations for divergence-free cleaning use in the eigenmode simulation type.

"EstimatorTol" [1.0e-6] : Relative tolerance for flux projection used in the error estimate calculation.

"EstimatorMaxIts" [10000] : Maximum number of iterations for flux projection use in the error estimate calculation.

"EstimatorMG" [false] : Set to true in order to enable multigrid preconditioner with AMG coarse solve for the error estimate linear solver, instead of just Jacobi.

"GSOrthogonalization" ["MGS"] : Gram-Schmidt variant used to explicitly orthogonalize vectors in Krylov subspace methods or other parts of the code.

  • "MGS" : Modified Gram-Schmidt
  • "CGS" : Classical Gram-Schmidt
  • "CGS2" : Two-step classical Gram-Schmidt with reorthogonalization

Advanced linear solver options

  • "InitialGuess" [true]
  • "MGUseMesh" [true]
  • "MGAuxiliarySmoother" [true]
  • "MGSmoothEigScaleMax" [1.0]
  • "MGSmoothEigScaleMin" [0.0]
  • "MGSmoothChebyshev4th" [true]
  • "ColumnOrdering" ["Default"] : "METIS", "ParMETIS","Scotch", "PTScotch", "PORD", "AMD", "RCM", "Default"
  • "STRUMPACKCompressionType" ["None"] : "None", "BLR", "HSS", "HODLR", "ZFP", "BLR-HODLR", "ZFP-BLR-HODLR"
  • "STRUMPACKCompressionTol" [1.0e-3]
  • "STRUMPACKLossyPrecision" [16]
  • "STRUMPACKButterflyLevels" [1]
  • "SuperLU3DCommunicator" [false]
  • "AMSVectorInterpolation" [false]
  • "AMSSingularOperator" [false]
  • "AMGAggressiveCoarsening" [false]