Model Functions Reference

This page lists the supported Exasim model functions and their interfaces. Text2Code uses capitalized names such as Flux; direct C++ model defaults use lower-case names such as flux. Provider code maps both forms into the same runtime ABI.

Common Arguments

Argument	Meaning
x	Spatial coordinates.
uq / udg	Packed solution and auxiliary gradient state.
v / odg	External or other-DG field.
w / wdg	Auxiliary state variables.
uhat / uhg	HDG trace state.
n / nlg	Outward normal on a face.
tau	Stabilization parameters.
mu / param	Physics parameters.
eta / uinf	Extra/reference/free-stream values.
t / time	Current time.
ib	Boundary-condition index.

Volume Functions

Text2Code	C++ model name	Output size	Purpose
Flux	flux	ncu * nd	Physical flux tensor.
Source	source	ncu	Volume source term.
Tdfunc	tdfunc	ncu	Time-derivative coefficient/mass term.
Avfield	avfield	model-dependent	Artificial-viscosity field.
Output	output	nce	User-defined DG output field.
Monitor	monitor	model-dependent	Runtime monitor field.

Text2Code form:

function Flux(x, uq, v, w, eta, mu, t)
  output_size(f) = ncu_times_nd;
  ...
end

C++ model form:

KOKKOS_INLINE_FUNCTION static
void flux(dstype f[], const dstype x[], const dstype uq[],
          const dstype v[], const dstype w[], const dstype mu[],
          const dstype uinf[], dstype t);

Boundary Functions

Text2Code	C++ model name	Output size	Purpose
Ubou	ubou	ncu	Boundary state/value.
Fbou	fbou	ncu	LDG boundary flux.
FbouHdg	fbou_hdg	ncu	HDG boundary residual/flux.
QoIboundary	qoi_boundary	boundary QoI count	Boundary QoI integrand.

Text2Code form:

function FbouHdg(x, uq, v, w, uhat, n, tau, eta, mu, t)
  output_size(fb) = ncu;
  ...
end

C++ model form:

KOKKOS_INLINE_FUNCTION static
void fbou_hdg(dstype fb[], int ib,
              const dstype x[], const dstype uq[],
              const dstype v[], const dstype w[], const dstype uh[],
              const dstype n[], const dstype tau[],
              const dstype mu[], const dstype uinf[], dstype t);

Initial Conditions

Text2Code	C++ model name	Output size	Purpose
Initu	initu	ncu	Initial primary state.
Initq	initq	ncu * nd	Initial gradient/auxiliary state.
Inituq	initudg	nc	Initial packed state.
Initw	initwdg	ncw	Initial auxiliary w.
Initv	initodg	nco	Initial external/other-DG field.

Initial-condition functions are important for parameter sweeps: if sol.bin does not contain a field, Exasim computes it using the active physicsparam for that run.

Auxiliary, EOS, and Visualization Functions

Text2Code	C++ model name	Output size	Purpose
Sourcew	sourcew	ncw	Auxiliary w source/evolution term.
EoS	eos	model-dependent	Closure/derived state.
VisScalars	vis_scalars	nsca	Scalar VTK fields.
VisVectors	vis_vectors	vector fields	Vector VTK fields.
VisTensors	vis_tensors	tensor fields	Tensor VTK fields.
QoIvolume	qoi_volume	nvqoi	Volume QoI integrand.

Coupling and Interface Functions

Text2Code	C++ model name	Purpose
Fint	interface provider callback	Interior/coupled-interface flux.
Fext	interface provider callback	External interface flux.
Provider Fhat	fhat	Coupled numerical flux hook.
Provider Uhat	uhat	Coupled trace hook.
Provider Stab	stab	Coupled stabilization hook.

These are advanced hooks used by coupled and multi-model workflows.

Jacobian Functions

HDG and derivative-enabled paths require Jacobian callbacks. Generated Text2Code providers derive these from declarations such as:

jacobian uq, w, uhat

Direct C++ models may override functions such as:

• flux_jac_uq
• flux_jac_w
• source_jac_uq
• source_jac_w
• fbou_jac_uq
• fbou_jac_uh
• fbou_jac_w
• ubou_jac_uq
• ubou_jac_uh
• ubou_jac_w
• fbou_hdg_jac_uq
• fbou_hdg_jac_uh
• fbou_hdg_jac_w

For HDG, incorrect or zero Jacobians can cause Newton or GMRES failure even if the value functions are correct.

ModelC, ModelD, and ModelW

Model type	Function implications
ModelC	Flux and Source depend primarily on u, optional w, v, and mu; no q + grad(u) equation is introduced.
ModelD	Flux may depend on q entries in uq; suitable for diffusion and mixed systems.
ModelW	uq includes wave auxiliary variables; Tdfunc and initialization must be consistent with wave evolution.

See Physics Models for mathematical details.