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muscl_eps #1383

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1f681f2
MUSCL
ChrisZYJ Apr 28, 2026
f5289ca
f_is_default and revert CMake changes
ChrisZYJ Apr 28, 2026
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5 changes: 5 additions & 0 deletions docs/documentation/case.md
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Expand Up @@ -445,6 +445,7 @@ See @ref equations "Equations" for the mathematical models these parameters cont
| `mp_weno` | Logical | Monotonicity preserving WENO |
| `muscl_order` | Integer | MUSCL order [1,2] |
| `muscl_lim` | Integer | MUSCL Slope Limiter: [1] minmod; [2] monotonized central; [3] Van Albada; [4] Van Leer; [5] SUPERBEE |
| `muscl_eps` | Real | MUSCL limiter slope-product threshold (default: hard-coded thresholds; set to 0 for textbook behavior) |
| `flux_lim` | Integer | Flux limiter for post-process: [1] minmod; [2] MUSCL; [3] OSPRE; [4] SUPERBEE |
| `int_comp` | Logical | THINC Interface Compression |
| `ic_eps` | Real | Interface compression threshold (default: 1e-4) |
Expand Down Expand Up @@ -542,6 +543,10 @@ It is recommended to set `weno_eps` to $10^{-6}$ for WENO-JS, and to $10^{-40}$
- `muscl_lim` specifies the slope limiter that is used in 2nd order MUSCL Reconstruction by an integer from 1 through 5.
`muscl_lim = 1`, `2`, `3`, `4`, and `5` correspond to minmod, monotonized central, Van Albada, Van Leer, and SUPERBEE, respectively.

- `muscl_eps` controls the slope-product activation threshold for all MUSCL limiters.
When not set (default), the threshold is 1e-9 for minmod/MC, and 1e-6 for others.
Setting `muscl_eps = 0` gives textbook limiter behavior where limiters activate whenever both slopes have the same sign.

- `int_comp` activates interface compression using THINC used in MUSCL Reconstruction, with control parameters (`ic_eps`, and `ic_beta`).

- `riemann_solver` specifies the choice of the Riemann solver that is used in simulation by an integer from 1 through 4.
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13 changes: 13 additions & 0 deletions src/simulation/m_global_parameters.fpp
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Expand Up @@ -148,6 +148,7 @@ module m_global_parameters
logical :: nv_uvm_pref_gpu !< Enable explicit gpu memory hints (default FALSE)
!> @}

real(wp) :: muscl_eps !< MUSCL limiter slope-product threshold
real(wp) :: weno_eps !< Binding for the WENO nonlinear weights
real(wp) :: teno_CT !< Smoothness threshold for TENO
logical :: mp_weno !< Monotonicity preserving (MP) WENO
Expand Down Expand Up @@ -197,6 +198,7 @@ module m_global_parameters
$:GPU_DECLARE(create='[recon_type, muscl_order, muscl_polyn, muscl_lim]')
#:endif

$:GPU_DECLARE(create='[muscl_eps]')
$:GPU_DECLARE(create='[mpp_lim, model_eqns, mixture_err, alt_soundspeed]')
$:GPU_DECLARE(create='[avg_state, mp_weno, weno_eps, teno_CT, hypoelasticity]')
$:GPU_DECLARE(create='[hyperelasticity, hyper_model, elasticity, low_Mach]')
Expand Down Expand Up @@ -521,6 +523,7 @@ contains
model_eqns = dflt_int
mpp_lim = .false.
time_stepper = dflt_int
muscl_eps = dflt_real
weno_eps = dflt_real
teno_CT = dflt_real
mp_weno = .false.
Expand Down Expand Up @@ -856,6 +859,15 @@ contains
$:GPU_UPDATE(device='[igr, igr_order, igr_iter_solver]')
#:endif

! muscl_eps: use per-limiter defaults when user did not set it
if (f_is_default(muscl_eps)) then
if (muscl_lim <= 2) then
muscl_eps = 1e-9_wp ! minmod, MC
else
muscl_eps = 1e-6_wp ! Van Albada, Van Leer, SUPERBEE
end if
end if

! Initialize counts: viscous fluids, surface-tension interfaces, curvature interfaces
Re_size = 0
Re_size_max = 0
Expand Down Expand Up @@ -1220,6 +1232,7 @@ contains
$:GPU_UPDATE(device='[num_fluids, num_dims, viscous, num_vels, nb, muscl_lim]')
#:endif

$:GPU_UPDATE(device='[muscl_eps]')
$:GPU_UPDATE(device='[dir_idx, dir_flg, dir_idx_tau]')

$:GPU_UPDATE(device='[relax, relax_model, palpha_eps, ptgalpha_eps]')
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11 changes: 5 additions & 6 deletions src/simulation/m_muscl.fpp
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Expand Up @@ -170,27 +170,26 @@ contains
slope = 0._wp

if (muscl_lim == 1) then ! minmod
if (slopeL*slopeR > 1e-9_wp) then
if (slopeL*slopeR > muscl_eps) then
slope = min(abs(slopeL), abs(slopeR))
end if
if (slopeL < 0._wp) slope = -slope
else if (muscl_lim == 2) then ! MC
if (slopeL*slopeR > 1e-9_wp) then
if (slopeL*slopeR > muscl_eps) then
slope = min(2._wp*abs(slopeL), 2._wp*abs(slopeR))
slope = min(slope, 5e-1_wp*(abs(slopeL) + abs(slopeR)))
end if
if (slopeL < 0._wp) slope = -slope
else if (muscl_lim == 3) then ! Van Albada
if (abs(slopeL) > 1e-6_wp .and. abs(slopeR) > 1e-6_wp .and. abs(slopeL + slopeR) &
& > 1e-6_wp .and. slopeL*slopeR > 1e-6_wp) then
if (slopeL*slopeR > muscl_eps) then
slope = ((slopeL + slopeR)*slopeL*slopeR)/(slopeL**2._wp + slopeR**2._wp)
end if
else if (muscl_lim == 4) then ! Van Leer
if (abs(slopeL + slopeR) > 1.e-6_wp .and. slopeL*slopeR > 1.e-6_wp) then
if (slopeL*slopeR > muscl_eps) then
slope = 2._wp*slopeL*slopeR/(slopeL + slopeR)
end if
else if (muscl_lim == 5) then ! SUPERBEE
if (slopeL*slopeR > 1e-6_wp) then
if (slopeL*slopeR > muscl_eps) then
slope = -1._wp*min(-min(2._wp*abs(slopeL), abs(slopeR)), -min(abs(slopeL), &
& 2._wp*abs(slopeR)))
end if
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2 changes: 1 addition & 1 deletion src/simulation/m_start_up.fpp
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Expand Up @@ -83,7 +83,7 @@ contains

namelist /user_inputs/ case_dir, run_time_info, m, n, p, dt, &
t_step_start, t_step_stop, t_step_save, t_step_print, &
model_eqns, mpp_lim, time_stepper, weno_eps, &
model_eqns, mpp_lim, time_stepper, weno_eps, muscl_eps, &
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@sbryngelson sbryngelson Apr 28, 2026

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2 vars -> 1 via reconst_eps which is either weno_eps or muscl_eps, depending on which method is used?

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@ChrisZYJ ChrisZYJ Apr 28, 2026

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I feel that we should keep "weno_eps" for backwards compatibility to not break existing case files, so maybe we can use weno_eps for both, or have both weno_eps and muscl_eps. Personally I feel that muscl_eps for MSUCL is cleaner?

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@sbryngelson sbryngelson Apr 29, 2026

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I think going to one, then updating all the case files at once via a sed replace (AI-friendly!) is fine.

rdma_mpi, teno_CT, mp_weno, weno_avg, &
riemann_solver, low_Mach, wave_speeds, avg_state, &
bc_x, bc_y, bc_z, &
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157 changes: 157 additions & 0 deletions tests/01DC0251/golden-metadata.txt
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12 changes: 12 additions & 0 deletions tests/01DC0251/golden.txt
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