Implement fit function back-to-back exponential convoluted with psuedo voigt

[wdzhou]

This issue was originally TRAC 8744

This ticket is blocks : TRAC8745

Implement a fit function back to back exponential convoluted with pseduo-voigt as an extension of existing fit function BackToBackExponential, which only is convoluted with Gaussian

[wdzhou]

@wdzhou (2014-01-31T04:03:47):
Starting to implement BackToBackExponentialPV. Refs http://trac.mantidproject.org/mantid/ticket/8744.

Starting to implement BackToBackExponentialPV.
The code is migrated from BacktoBackExponential.
Some changes have been implemented.
But it is not finished yet.

6659add

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@NickDraper (2014-02-02T15:34:46):
Moved to backlog at the end of Release 3.1

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@wdzhou (2014-02-03T16:48:23):
Finished implementation of the function. Refs http://trac.mantidproject.org/mantid/ticket/8744.

936c2af

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@wdzhou (2014-02-03T21:13:45):
Added some unit tests. Refs http://trac.mantidproject.org/mantid/ticket/8744.

eba451a

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@wdzhou (2014-02-05T19:36:36):
Fixed unit test. Refs http://trac.mantidproject.org/mantid/ticket/8744.

f5e62cc

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@wdzhou (2014-02-13T21:18:21):
Modified doc in wiki. Refs http://trac.mantidproject.org/mantid/ticket/8744.

3e4d8f8

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@wdzhou (2014-02-13T21:18:21):
Added one more unit test. Refs http://trac.mantidproject.org/mantid/ticket/8744.

97afd4e

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@wdzhou (2014-02-14T14:37:46):
Minor modification on how to calculate peak extent. Refs http://trac.mantidproject.org/mantid/ticket/8744.

e204f6b

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@wdzhou (2014-02-14T14:39:42):
== For tester ==
Find some data from instruments using back-to-back exponential convoluted with pseudo-voigt as peak profile. Then using this function to fit some peak.

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@Anders-Markvardsen (2014-02-18T10:12:38):
ISIS HRPD focused processed nexus file

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@Anders-Markvardsen (2014-02-18T10:27:42):

1. Load attached hrp55500.nxs file
2. Plot workspace hrp55500_2 for example
3. Add LinearBackground and one BackToBackExponentialPV peak

When I try to adjust the width graphically I get the error message "Peak width cannot be equal or less than zero", see attaced picture1.png

In another attempt, good new is that I did get a fit, but the parameters ! and B does not change. Also if I change the values of these manually as far as I can tell the peak shape does not change when I do plot guess.

When I select a non-zero value for Gamma, e.g. 1.0, and then to a fit I, the fit takes a lot longer and a lot of red lines are outputted, e.g:

rying to set a NaN or infinity value (1.#QNAN) to parameter Gamma
Trying to set a NaN or infinity value (1.#QNAN) to parameter I
Trying to set a NaN or infinity value (1.#QNAN) to parameter A
Trying to set a NaN or infinity value (1.#QNAN) to parameter B
Trying to set a NaN or infinity value (1.#QNAN) to parameter X0
Trying to set a NaN or infinity value (1.#QNAN) to parameter S
Trying to set a NaN or infinity value (1.#QNAN) to parameter Gamma
Trying to set a NaN or infinity value (1.#QNAN) to parameter I
Trying to set a NaN or infinity value (1.#QNAN) to parameter A
Trying to set a NaN or infinity value (1.#QNAN) to parameter B
Trying to set a NaN or infinity value (1.#QNAN) to parameter X0
Trying to set a NaN or infinity value (1.#QNAN) to parameter S
Trying to set a NaN or infinity value (1.#QNAN) to parameter Gamma
Trying to set a NaN or infinity value (1.#QNAN) to parameter I
Trying to set a NaN or infinity value (1.#QNAN) to parameter A
Trying to set a NaN or infinity value (1.#QNAN) to parameter B
Trying to set a NaN or infinity value (1.#QNAN) to parameter X0
Trying to set a NaN or infinity value (1.#QNAN) to parameter S
Trying to set a NaN or infinity value (1.#QNAN) to parameter Gamma
Trying to set a NaN or infinity value (1.#QNAN) to parameter I
Trying to set a NaN or infinity value (1.#QNAN) to parameter A
Trying to set a NaN or infinity value (1.#QNAN) to parameter B
Trying to set a NaN or infinity value (1.#QNAN) to parameter X0
Trying to set a NaN or infinity value (1.#QNAN) to parameter S
Trying to set a NaN or infinity value (1.#QNAN) to parameter Gamma
Trying to set a NaN or infinity value (1.#QNAN) to parameter I
Trying to set a NaN or infinity value (1.#QNAN) to parameter A
Trying to set a NaN or infinity value (1.#QNAN) to parameter B
Trying to set a NaN or infinity value (1.#QNAN) to parameter X0
Trying to set a NaN or infinity value (1.#QNAN) to parameter S
Trying to set a NaN or infinity value (1.#QNAN) to parameter Gamma
Trying to set a NaN or infinity value (1.#QNAN) to parameter I
Trying to set a NaN or infinity value (1.#QNAN) to parameter A
Trying to set a NaN or infinity value (1.#QNAN) to parameter B
Trying to set a NaN or infinity value (1.#QNAN) to parameter X0
Trying to set a NaN or infinity value (1.#QNAN) to parameter S
Trying to set a NaN or infinity value (1.#QNAN) to parameter Gamma
Trying to set a NaN or infinity value (1.#QNAN) to parameter I

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@NickDraper (2014-12-08T10:25:31):
Moved to the backlog at the code freeze of R3.3

[wdzhou]

http://trac.mantidproject.org/mantid/raw-attachment/ticket/8744/hrp55500.nxs
(uploaded by @Anders-Markvardsen on 2014-02-18T10:12:38)

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http://trac.mantidproject.org/mantid/raw-attachment/ticket/8744/picture1.png

(uploaded by @Anders-Markvardsen on 2014-02-18T10:28:02)

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[FedeMPouzols]

We have a function called Bk2BkExpConvPV which is available in Mantid. What's the difference between Bk2BkExpConvPV and the one proposed in this ticket (BackToBackExponentialPV)?

@Anders-Markvardsen : for documentation purposes it would be nice to clarify what "back-to-back exponential / convoluted with..." functions are available, their variants and how exactly they're defined in Mantid (equations and references). There are no documentation pages for these functions, but we have this wiki page: http://www.mantidproject.org/BackToBackExponentialPV

Related to this, there are these two other functions: NeutronBk2BkExpConvPVoigt and ThermalNeutronBk2BkConvPVoigt (#9589).

[Anders-Markvardsen]

@FedeMPouzols there is a rst for BackToBackExponential, see http://docs.mantidproject.org/nightly/fitfunctions/BackToBackExponential.html for its wiki translation.

You can also find this documentation by clicking on 'Fit functions' on http://www.mantidproject.org/Documentation.

@wdzhou is this issue now a duplicate? I.e. has this function has now been implemented as Bk2BkExpConvPV?

The wiki http://www.mantidproject.org/BackToBackExponentialPV was probably written before we introduced rst documentation for fit functions, and this wiki page should be deleted and its content used for a rst documentation page for the back to back exp PV fit function implementation

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