class zfit.loss.BaseLoss(model, data, fit_range=None, constraints=None, options=None)[source]#

Bases: ZfitLoss, BaseNumeric

A “simultaneous fit” can be performed by giving one or more model, data, fit_range to the loss. The length of each has to match the length of the others.

  • model (ztyping.ModelsInputType) – The model or models to evaluate the data on

  • data (ztyping.DataInputType) – Data to use

  • fit_range (ztyping.LimitsTypeInput) – The fitting range. It’s the norm_range for the models (if they have a norm_range) and the data_range for the data.

  • constraints (ztyping.ConstraintsTypeInput) – A Tensor representing a loss constraint. Using zfit.constraint.* allows for easy use of predefined constraints.

  • options (Mapping | None) – Different options for the loss calculation.


Calculate the loss value with the given input for the free parameters.


*positional* – Array-like argument to set the parameters. The order of the values correspond to the position of the parameters in get_params() (called without any arguments). For more detailed control, it is always possible to wrap value() and set the desired parameters manually.

Return type



Calculated loss value as a scalar.

add_cache_deps(cache_deps, allow_non_cachable=True)#

Add dependencies that render the cache invalid if they change.

  • cache_deps (Union[zfit.core.interfaces.ZfitGraphCachable, Iterable[zfit.core.interfaces.ZfitGraphCachable]]) –

  • allow_non_cachable (bool) – If True, allow cache_dependents to be non-cachables. If False, any cache_dependents that is not a ZfitGraphCachable will raise an error.


TypeError – if one of the cache_dependents is not a ZfitGraphCachable _and_ allow_non_cachable if False.

property dtype: DType#

The dtype of the object.

Return type



Return a set of all independent Parameter that this object depends on.


only_floating (bool) – If True, only return floating Parameter

Return type




Deprecated: THIS FUNCTION IS DEPRECATED. It will be removed in a future version. Instructions for updating: Use get_params instead if you want to retrieve the independent parameters or get_cache_deps in case you need the numerical cache dependents (advanced).

Return type


get_params(floating=True, is_yield=None, extract_independent=True, only_floating=<class 'zfit.util.checks.NotSpecified'>)#

Recursively collect parameters that this object depends on according to the filter criteria.

Which parameters should be included can be steered using the arguments as a filter.
  • None: do not filter on this. E.g. floating=None will return parameters that are floating as well as

    parameters that are fixed.

  • True: only return parameters that fulfil this criterion

  • False: only return parameters that do not fulfil this criterion. E.g. floating=False will return

    only parameters that are not floating.

  • floating (bool | None) – if a parameter is floating, e.g. if floating() returns True

  • is_yield (bool | None) – if a parameter is a yield of the _current_ model. This won’t be applied recursively, but may include yields if they do also represent a parameter parametrizing the shape. So if the yield of the current model depends on other yields (or also non-yields), this will be included. If, however, just submodels depend on a yield (as their yield) and it is not correlated to the output of our model, they won’t be included.

  • extract_independent (bool | None) – If the parameter is an independent parameter, i.e. if it is a ZfitIndependentParameter.

Return type



Register a cacher that caches values produces by this instance; a dependent.


cacher (Union[zfit.core.interfaces.ZfitGraphCachable, Iterable[zfit.core.interfaces.ZfitGraphCachable]]) –


Clear the cache of self and all dependent cachers.