5. Parameters

Parameters can be set using the commands in Material Commands. There are two complementary formalisms for doing this.

5.1. Parameters

Parameters are set globally, on devices, or on regions of a device. The models on each device region are automatically updated whenever parameters change.

devsim.set_parameter(device="device", region="region",
  name="ThermalVoltage", value=0.0259)

They may also be used to control program behavior, as listed in Table 5.1:

Table 5.1 Parameters controlling program behavior.
Parameter	Description
`debug_level`	`info`, `verbose` Section 9.3.5
`threads_available`	`value=1`, Section 9.3.6
`threads_task_size`	`value=?`, Section 9.3.6
`node_volume_model`	Section 4.6
`edge_couple_model`	Section 4.6
`edge_node0_volume_model`	Section 4.6
`edge_node1_volume_model`	Section 4.6
`element_edge_couple_model`	Section 4.6
`element_node0_volume_model`	Section 4.6
`element_node1_volume_model`	Section 4.6
`extended_solver`	`value=False` Extended precision matrix and RHS assembly and error evaluations. Linear solver and circuit assembly is still double precision``
`extended_model`	`value=False` Extended precision model evaluation
`extended_equation`	`value=False` Extended precision equation evaluation
`surface_area_model`	Model for integration of flux and hybrid interfaces.

5.2. Environment Variables

Environment variables to control program behavior are listed in Table 5.2:. Please consult Section 2: for the most up to information concerning their usage.

Table 5.2 Environment controlling program behavior.
Environment Variable	Description
`DEVSIM_MATH_LIBS`	List of BLAS/LAPACK libraries to load instead of system defaults
`DEVSIM_NEW_SYMBOLIC`	When set, do a new symbolic matrix factorization during direct solve iterations

5.3. Material database entries

Alternatively, parameters may be set based on material types. A database file is used for getting values on the regions of the device.

devsim.create_db(filename="foodb")
devsim.add_db_entry(material="global", parameter="q", value=1.60217646e-19,
  unit="coul", description="Electron Charge")
devsim.add_db_entry(material="Si", parameter="one",
  value=1, unit="", description="")
devsim.close_db

When a database entry is not available for a specific material, the parameter will be looked up on the global material entry.

5.4. Discussion

Both parameters and material database entries may be used in model expressions. Parameters have precedence in this situation. If a parameter is not found, then DEVSIM will also look for a circuit node by the name used in the model expression.