Internal parameters¶

This section provides an overview of all the internal FastChem parameters that can be adjusted via the aforementioned

void FastChem.setParameter(std::string param_name,
                           param_type param_value)

method of the C++ object class or with its Python equivalent

pyfastchem.setParameter(str param_name,
                        param_type param_value)

More detailed explanations of what these parameters do can be found in Stock et al. (2018), Stock, Kitzmann & Patzer (2022), and Kitzmann, Stock & Patzer (2024)

When using the setParameter method in Python, the C++double types listed below should be replaced by Python float values, while unsigned int should be passed as int. Python bool values (True/False) are correctly dispatched to the bool overload without requiring explicit conversion.

Standard parameters¶

accuracyChem

Relative accuracy requirement for chemistry iteration and internal solvers (except Newton’s method).
Type: double
Default value: 1e-5

accuracyElementConservation

Relative accuracy for checking the element conservation.
Type: double
Default value: 1e-4

accuracyNewton

Relative accuracy requirement for Newton’s method.
Type: double
Default value: 1e-5

accuracyCond

Relative accuracy requirement for condensation calculations.
Type: double
Default value: 1e-5

nbIterationsChemCond

Maximum number of combined gas phase chemistry and condensate calculations.
Type: unsigned int
Default value: 3000

nbIterationsChem

Maximum number of chemistry iterations.
Type: unsigned int
Default value: 3000

nbIterationsCond

Maximum number of condensate calculation iterations.
Type: unsigned int
Default value: 3000

nbSwitchToNewton

Number of iterations above which the gas phase calculations switch to a multi-dimensional Newton’s method.
Type: unsigned int
Default value: 400

nbIterationsNewton

Maximum number of iterations for Newton’s method.
Type: unsigned int
Default value: 3000

nbIterationsBisection

Maximum number of iterations for the bisection method.
Type: unsigned int
Default value: 3000

nbIterationsNelderMead

Maximum number of iterations for the Nelder-Mead method.
Type: unsigned int
Default value: 3000

Advanced parameters¶

The following parameters can be considered potentially dangerous and should only be adjusted by users who know exactly what these parameters actually do and which side effects they may have.

minDensityExponentElement

Exponent for the minimum number density of elements.
Type: double
Default value: -155

minDensityExponentMolecules

Exponent for the minimum number density of molecules and ions.
Type: double
Default value: -155

condTau

Baseline \(\tau\) value for condensates.
Type: double
Default value: 1e-15

condIterChangeLimit

Maximum change of condensate densities per iteration step in log10 space.
Type: double
Default value: 5

condReduceSystemSize

Reduce the size of the condensate system of equations by removing unstable condensates.
Type: bool
Default value: true

condUseSVD

Solve the condensate system of equations using a singular value decomposition (SVD) when the Jacobian is singular.
Type: bool
Default value: false

useCondDataValidityLimit

Use data temperature limits from the condensate input file and avoid extrapolation outside the validity range of the fitted data. Outside the validity range, the activity of condensates is automatically set to a very small value.
Type: bool
Default value: true

condUseLM

Use a Levenberg–Marquardt regularisation for the condensate Newton solver. When the Jacobian is singular or near-singular (e.g. fully depleted trace elements after rainout), the solver switches from a plain LU decomposition to the LM normal equations to obtain a well-defined step.
Type: bool
Default value: true

nbSwitchToJoint

Maximum number of combined gas phase / condensate outer-loop iterations before the solver switches to a joint gas+condensate Newton step. The joint step is also activated adaptively when stagnation or divergence is detected. Setting this to a large value effectively disables the fixed trigger.
Type: unsigned int
Default value: 3000

condTraceDensityThreshold

Threshold for the maximum possible number density of a condensate (in cm-3). Condensates whose maximum possible number density (computed from element abundances and stoichiometry) falls below this value are excluded from the condensate Newton solver and their number density is set to zero. This avoids Jacobian ill-conditioning caused by trace elements that have been nearly completely rained out.
Type: double
Default value: 1e-100