Sum|Multi(p1,p2) does not work

[gonzalezm]

Sum (multiplication) of two models does not work (known bug, reported also by thomas.cleveland@…)

When trying to create a model as the sum of two standard models, the following error message appears:

“Running model 'MySumFunction.py'…
Error occurred:
Traceback (most recent call last):

File "sas\sasgui\perspectives\calculator\pyconsole.pyc", line 55, in show_model_output
File "sas\sasgui\perspectives\calculator\pyconsole.pyc", line 30, in check_model

ImportError: cannot import name make_class”

This happens because the function make_class (in sasmodels/sasview_model.py) does not exist anymore, as it was replaced by _make_standard_model in 4d76711 on Apr 5 (Paul Kienzle adjust interface to sasview). Note: The comment at the beginning of sasview_model.py should be changed accordingly, as it still mentions make_class.

The obvious change that I tried is to replace make_class by _make_standard_model in the python file generated by “Sum|Multi(p1,p2)”, but then a different problem happens and the fitting perspective is broken, so it is even worse than the original bug.

This is what I could follow about the program execution:

• I start SasView 4.0 having the file MG_sum1.py in the .sasview\plugin_models folder. This is just the file created by the template of “Sum|Multi(p1,p2)” for a model consisting of an sphere + a cylinder, but replacing make_class by _make_standard_model.

• In sasview\src\sas\sasgui\perspectives\fitting\models.py it is added to the plugins by the command plugins[name] = module.Model, returning a class MG_sum1.model. As a reference, a simple python model present in the plugin_models is loaded using plugins[name] = load_custom_model(filename) and we generate a class sasmodels.sasview_model.MG_simple1

• In the call to _get_multifunc_models, an error is generated because the class Model has no attribute ‘is_multiplicitiy_model’

[ajj]

There is a cascading set of changes in the model interface that means that I don't think we can make a sum/multi model the way we do now.

I tried changing the call to make_class to load_standard_models which seems to allow the model to get further, but fails on pyconsole.check_model()

This is because of the way that load_model_info now works - it attempts to handle + and * models by parsing the model name.

Thus a sum/multi model does not exist anymore as a separate entity - not clear how we can change the infrastructure to support these "virtual" models and have them be persistent.

Should probably be encouraging users to write models that re-parameterise and then call underlying model kernels but again it is not clear (to me) how to do this with the current approach.

[pkienzle]

I made the current approach work again for alpha, but still want to refactor it for beta, time permitting, so that sum and multiply are more compact. I'll open this as a new ticket.