# Parameters: Simulation

Command ElementModifies the simulation parameter element.

## Format

<Param_Simulation
[ constr_tol          = "real" ]
[ implicit_diff_tol   = "real" ]
[ nr_converge_ratio   = "real" ]
[ linsolver           = "HARWELL" ]
[ acusolve_cosim      = "TRUE | FALSE" ]
/>

## Attributes

constr_tol
Modifies the accuracy to which the system configuration and motion constraints are to be satisfied at each step. This is used by kinematics and the transient solver in ODE formulation (ABAM, VSTIFF, or MSTIFF), but not the DAE form, which has its own tolerance for this (Param_Transient::dae_constr_tol). This should be a small positive number.
The default value for constr_tol = 1.0E-10.
implicit_diff_tol
Modifies the accuracy to which implicit differential equations, such as Control_Diff equations with the is_implicit = "TRUE", are to be satisfied. The default value for implicit_diff_tol = 1.0E-5.
nr_converg_ratio
Modifies a measure of the rate of convergence in the Newton-Raphson method for ODE solvers. If the maximum entry in the constraint vector is larger than nr_converg_ratio times the maximum entry from the previous iteration, the Newton-Raphson iterations are converging slowly and the generalized coordinates will be re-partitioned in the next integration step to select a new set of independent coordinates. This attribute is applicable only if an ODE integrator (ABAM, VSTIFF, or MSTIFF) is selected.
The default value is 0.09.
linsolver
The type of linear solver used, which currently is set to "HARWELL" for all analyses.
acusolve_cosim
A Boolean flag that determines whether the simulation will be coupled with AcuSolve or not.
"TRUE" means that the MBD model is to be coupled with the CFD model in a co-simulation between MotionSolve and AcuSolve.
"FALSE" means that the MBD model is not to be coupled with the CFD model.
The default value is "FALSE".

## Example

The example below shows the default settings for the Param_Simulation command element.

<Param_Simulation
constr_tol          = "1E-10"
implicit_diff_tol   = "1E-5"
nr_converg_ratio    = "0.09"
linsolver           = "HARWELL"
/>