# Modifying Internal QuTiP Settings¶

## User Accessible Parameters¶

In this section we show how to modify a few of the internal parameters used by QuTiP. The settings that can be modified are given in the following table:

Setting

Description

Options

auto_herm

Automatically calculate the hermicity of quantum objects.

True / False

auto_tidyup

Automatically tidyup quantum objects.

True / False

auto_tidyup_atol

Tolerance used by tidyup

any float value > 0

atol

General tolerance

any float value > 0

num_cpus

Number of CPU’s used for multiprocessing.

int between 1 and # cpu’s

debug

Show debug printouts.

True / False

openmp_thresh

NNZ matrix must have for OPENMP.

Int

## Example: Changing Settings¶

The two most important settings are auto_tidyup and auto_tidyup_atol as they control whether the small elements of a quantum object should be removed, and what number should be considered as the cut-off tolerance. Modifying these, or any other parameters, is quite simple:

>>> qutip.settings.auto_tidyup = False


These settings will be used for the current QuTiP session only and will need to be modified again when restarting QuTiP. If running QuTiP from a script file, then place the qutip.setings.xxxx commands immediately after from qutip import * at the top of the script file. If you want to reset the parameters back to their default values then call the reset command:

>>> qutip.settings.reset()


## Persistent Settings¶

When QuTiP is imported, it looks for a file named qutiprc in a folder called .qutip user’s home directory. If this file is found, it will be loaded and overwrite the QuTiP default settings, which allows for persistent changes in the QuTiP settings to be made. A sample qutiprc file is show below. The syntax is a simple key-value format, where the keys and possible values are described in the table above:

[qutip]
auto_tidyup=True
auto_herm=True
auto_tidyup_atol=1e-12
num_cpus=4
debug=False


Note that the openmp_thresh value is automatically generatd by QuTiP. It is also possible to set a specific compiler for QuTiP to use when generating runtime Cython code for time-dependent problems. For example, the following section in the qutiprc file will set the compiler to be clang-3.9:

[compiler]
cc = clang-3.9
cxx = clang-3.9