The following variables can be set from the netlist using the
`.options` keyword. Available options are listed below:

Name Default Unit Description abstol 1e-07 nodal unit Absolute tolerance for nodal variables errfunc 0 bool Enable additional test for error function in Newton’s method gyr 0.001 S Default gain in internal gyrators maxdelta 20.0 nodal unit Maximum allowed change in one Newton iteration maxiter 20 Maximum number of Newton iterations reltol 0.0001 Relative tolerance for nodal variables sparse 1 bool Use sparse matrices in analyses if possible temp 27.0 C Ambient temperature

Global options can be accessed within an interactive shell in the program. For example:

```
cechrist@moon:~/$ cardoon -i
Cardoon Circuit Simulator 0.4 release 0.4.1.dev
Type CTR-D to exit
In <1>: glVar.gyr
Out<1>: 0.001
In <2>: glVar.abstol
Out<2>: 1e-08
In <3>:
```

`abstol`and`reltol`control the absolute and relative tolerances in nodal variables. Iterations stop when updates in nodal variables are smaller than`abstol + reltol * var`.- If
`errfunc`is set then an additional test is performed to check that the error in the nodal equation is less than`abstol`. This test is disabled by default because it introduces additional overhead. However it may be useful in cases where convergence is very slow. - The
`gyr`variable is used to control the gain of internal gyrators in some device models. For example, a value of 1e-3 means that the extra nodal voltage in an ideal voltage source model is equal to the current through the source expressed in mA. - Sometimes Newton’s method convergence can be achieved by adjusting
the value of
`maxdelta`and increasing`maxiter`.

Physical constants are used within models and they are also available from interactive shells:

```
In <4>: from globalVars import const
In <5>: const.epsilon0
Out<5>: 8.8541878170000005e-12
```

Table of physical and mathematical constants:

Name Default Unit Description Np2dB 8.68588963807 dB/Np Neper to dB conversion constant T0 273.15 K Zero degree Celsius temperature c0 299792458.0 m s^{-1} Speed of light in free space epOx 3.45e-11 Permitivity of silicon oxide epSi 1.045e-10 Permitivity of silicon epsilon0 8.854187817e-12 F m^{-1} Permittivity of free space k 1.3806488e-23 J K^{-1} Boltzmann constant mu0 1.25663706144e-06 H m^{-1} Permeability of free space q 1.602176565e-19 C Elementary charge