calculate all I(q) values needed for 1D resolution in one call (Trac #717)

[pkienzle]

When I(q) is computed with resolution, the theory values are first computed for the measured points, then another call is made to compute the points before the first measured point and another call is made to compute the points after the last measured point. This will significantly slow down the throughput on the GPU for simple models, where the overhead of three calls will be larger than cost of the calls.

This is one step toward refactoring the fitting perspective to more cleanly separate computation from user interface.

See code in:

    sas.sascalc.data_util.qsmearing.PySmear.apply

called from:

     sas.sasgui.perspectives.fitting.model_thread.Calc1D.compute
     sas.sascalc.fit.AbstractFitEngine.FitData1D.residuals

Migrated from http://trac.sasview.org/ticket/717

{
    "status": "new",
    "changetime": "2017-03-08T17:03:14",
    "_ts": "2017-03-08 17:03:14.148073+00:00",
    "description": "When I(q) is computed with resolution, the theory values are first computed for the measured points, then another call is made to compute the points before the first measured point and another call is made to compute the points after the last measured point.  This will significantly slow down the throughput on the GPU for simple models, where the overhead of three calls will be larger than cost of the calls.\n\nThis is one step toward refactoring the fitting perspective to more cleanly separate computation from user interface.\n\nSee code in:\n{{{\n    sas.sascalc.data_util.qsmearing.PySmear.apply\n}}}\ncalled from:\n{{{\n     sas.sasgui.perspectives.fitting.model_thread.Calc1D.compute\n     sas.sascalc.fit.AbstractFitEngine.FitData1D.residuals\n}}}",
    "reporter": "pkienzle",
    "cc": "",
    "resolution": "",
    "workpackage": "SasView Bug Fixing",
    "time": "2016-10-06T16:42:12",
    "component": "SasView",
    "summary": "calculate all I(q) values needed for 1D resolution in one call",
    "priority": "major",
    "keywords": "",
    "milestone": "SasView Next Release +1",
    "owner": "",
    "type": "defect"
}

[pkienzle]

Trac update at 2016/10/10 18:25:09: pkienzle commented:

Also, separate model setup from model call so that model+q is initialized before fit and reused for each step of the computation. In sasmodels.sasview_model.SasviewModel.calculateIq the model is being loaded from file and released each call (DLL), and a new q vector is being created each call (OpenCL).

[pkienzle]

Trac update at 2017/03/08 17:03:14: pkienzle commented:

With q_calc completely independent of q we can increase the sampling density between q values as needed for the resolution. See ticket SasView/sasmodels#263.

Maybe put oversampling under user control. If fitting a system of large mono-disperse particles, we ought to sample q more densely than the fringe spacing in the model when computing the resolution. This allows users to work around the issue that sasmodels does not do adaptive integration for resolution. See ticket SasView/sasmodels#535.