sherpa.astro.ui.load_user_model(func, modelname, filename=None, *args, **kwargs)

Create a user-defined model.

Assign a name to a function; this name can then be used as any other name of a model component, either in a source expression - such as with set_model - or to change a parameter value. The add_user_pars function should be called after load_user_model to set up the parameter names and defaults.

  • func (func) – The function that evaluates the model.

  • modelname (str) – The name to use to refer to the model component.

  • filename (str, optional) – Set this to include data from this file in the model. The file should contain two columns, and the second column is stored in the _y attribute of the model.

  • args – Arguments for reading in the data from filename, if set. See load_table and load_image for more information.

  • kwargs – Keyword arguments for reading in the data from filename, if set. See load_table and load_image for more information.

See also


Create a user-defined model class.


Add parameter information to a user model.


Load an image as a data set.


Load a FITS binary file as a data set.


Load tabular data and use it as a model component.


Load a set of templates and use it as a model component.


Set the source model expression for a data set.


The load_user_model function is designed to make it easy to add a model, but the interface is not the same as the existing models (such as having to call both load_user_model and add_user_pars for each new instance). The add_model function is used to add a model as a Python class, which is more work to set up, but then acts the same way as the existing models.

The function used for the model depends on the dimensions of the data. For a 1D model, the signature is:

def func1d(pars, x, xhi=None):

where, if xhi is not None, then the dataset is binned and the x argument is the low edge of each bin. The pars argument is the parameter array - the names, defaults, and limits can be set with add_user_pars - and should not be changed. The return value is an array the same size as x.

For 2D models, the signature is:

def func2d(pars, x0, x1, x0hi=None, x1hi=None):

There is no way using this interface to indicate that the model is for 1D or 2D data.


Create a two-parameter model of the form “y = mx + c”, where the intercept is the first parameter and the slope the second, set the parameter names and default values, then use it in a source expression:

>>> def func1d(pars, x, xhi=None):
...     if xhi is not None:
...         x = (x + xhi)/2
...     return x * pars[1] + pars[0]
>>> load_user_model(func1d, "myfunc")
>>> add_user_pars(myfunc, ["c", "m"], [0, 1])
>>> set_source(myfunc + gauss1d.gline)