General Settings

In this section, we discuss some settings that can be included in Colibri runcards that are relevant to any type of fit.

Imposing Positivity Constraints on a Fit

This section describes how to impose positivity constraints on a Colibri PDF fit.

You may have noticed these settings on some of the runcards shown in the previous tutorials:

positivity:                            # Positivity datasets, used in the positivity penalty.
    posdatasets:
    - {dataset: NNPDF_POS_2P24GEV_F2U, variant: None, maxlambda: 1e6}

positivity_penalty_settings:
    positivity_penalty: false
    alpha: 1e-7
    lambda_positivity: 0

To impose positivity constraints on a PDF fit, you can simply set positivity_penalty to true. You can also add more detasets under posdatasets.

positivity_penalty_settings

• alpha: Defaults to 1e-07.

• lambda_positivity: Defaults to 3000.