Damped GaussNewton minimizer with ties crashes on Crystal Field Example

[jfowkes]

Running the Crystal Field example from the docs on Mantid 6.0 as follows:

import mantid.simpleapi as mt

# Load crystal field data
data_ws1 = mt.Load('NdOs2Al10_5K35meV_Ecut_0to3ang_bp15V1.xye')

# Setup crystal field model
cf = mt.CrystalFieldSpectrum(Ion='Nd', Symmetry='C2v', Temperature=5., FWHM=1., B20=0.19, B22=0.11,
                             B40=-0.0004, B42=-0.002, B44=-0.012, B60=5.e-5, B62=0.00054, B64=-0.0006, 
                             B66=0.0008, PeakShape='Lorentzian', IntensityScaling=2.)

# Fix molecular and external magnetic fields
for magfieldPars in ['BmolX', 'BmolY', 'BmolZ', 'BextX', 'BextY', 'BextZ']:
    cf.function.tie(magfieldPars, '0')
# Fix B66 
cf.function.tie('B66','0.0008')

# Run fit
fit = mt.Fit(cf, InputWorkspace=data_ws1, Minimizer='Damped GaussNewton', MaxIterations=100, Output='fit')

crashes with the following traceback:

Fit-[Notice] Fit started

********* UNHANDLED EXCEPTION *********
  what(): GSLVector index = 26 is out of range = 26 in GSLVector.get()

Backtrace:
 /opt/Mantid/lib/mantid/api/../../../lib/libMantidAPI.so(+0x1ba5f9) [0x7feb468c15f9]
 /opt/Mantid/lib/mantid/api/../../../lib/libMantidAPI.so(+0x1ba7ca) [0x7feb468c17ca]
 /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x92ae6) [0x7febb0b67ae6]
 /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x91b49) [0x7febb0b66b49]
 /usr/lib/x86_64-linux-gnu/libstdc++.so.6(__gxx_personality_v0+0x2a8) [0x7febb0b674b8]
 /lib/x86_64-linux-gnu/libgcc_s.so.1(+0x10573) [0x7febb08cd573]
 /lib/x86_64-linux-gnu/libgcc_s.so.1(_Unwind_Resume+0x125) [0x7febb08cddf5]
 /opt/Mantid/plugins/libMantidCurveFitting.so(_ZNK6Mantid12CurveFitting9GSLVector3getEm+0x148) [0x7feb1409fd58]
 /opt/Mantid/plugins/libMantidCurveFitting.so(_ZNK6Mantid12CurveFitting13CostFunctions20CostFuncLeastSquares18addValDerivHessianESt10shared_ptrINS_3API9IFunctionEES3_INS4_14FunctionDomainEES3_INS4_14FunctionValuesEEbb+0x249) [0x7feb13f607c9]
 /opt/Mantid/plugins/libMantidCurveFitting.so(_ZNK6Mantid12CurveFitting13CostFunctions15CostFuncFitting15valDerivHessianEbb+0x3d1) [0x7feb13f5fb41]
 /opt/Mantid/plugins/libMantidCurveFitting.so(_ZN6Mantid12CurveFitting14FuncMinimisers26DampedGaussNewtonMinimizer7iterateEm+0x17e) [0x7feb13f6a6ee]
 /opt/Mantid/plugins/libMantidCurveFitting.so(_ZN6Mantid12CurveFitting10Algorithms3Fit12runMinimizerEv+0x1ac) [0x7feb13e711ec]
 /opt/Mantid/plugins/libMantidCurveFitting.so(_ZN6Mantid12CurveFitting10Algorithms3Fit12execConcreteEv+0x38) [0x7feb13e73948]
 /opt/Mantid/plugins/libMantidCurveFitting.so(_ZN6Mantid12CurveFitting17IFittingAlgorithm4execEv+0xad) [0x7feb140ab5dd]
 /opt/Mantid/lib/mantid/api/../../../lib/libMantidAPI.so(_ZN6Mantid3API9Algorithm4execENS_8Parallel13ExecutionModeE+0x43) [0x7feb46827313]
 /opt/Mantid/lib/mantid/api/../../../lib/libMantidAPI.so(_ZN6Mantid3API9Algorithm15executeInternalEv+0x39f) [0x7feb468284cf]
 /opt/Mantid/lib/mantid/api/_api.so(+0xc73ee) [0x7feb46d373ee]
 /opt/Mantid/lib/mantid/api/_api.so(+0xce07a) [0x7feb46d3e07a]
 /usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1(_ZNK5boost6python7objects8function4callEP7_objectS4_+0x285) [0x7feb4debd855]
 /usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1(+0x21a18) [0x7feb4debda18]
 /usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1(_ZNK5boost6python6detail17exception_handlerclERKNS_9function0IvEE+0x6b) [0x7feb4dec45db]
 /opt/Mantid/lib/mantid/api/_api.so(+0xe7193) [0x7feb46d57193]
 /usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1(_ZNK5boost6python6detail17exception_handlerclERKNS_9function0IvEE+0x3a) [0x7feb4dec45aa]
 /opt/Mantid/lib/mantid/api/_api.so(+0xe7193) [0x7feb46d57193]
 /usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1(_ZNK5boost6python6detail17exception_handlerclERKNS_9function0IvEE+0x3a) [0x7feb4dec45aa]
 /opt/Mantid/lib/mantid/api/_api.so(+0xe7193) [0x7feb46d57193]
 /usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1(_ZNK5boost6python6detail17exception_handlerclERKNS_9function0IvEE+0x3a) [0x7feb4dec45aa]
 /opt/Mantid/lib/mantid/api/_api.so(+0xe7193) [0x7feb46d57193]
 /usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1(_ZN5boost6python21handle_exception_implENS_9function0IvEE+0x3f) [0x7feb4dec437f]
 /usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1(+0x1f119) [0x7feb4debb119]
 /usr/bin/python3(_PyObject_FastCallKeywords+0x19c) [0x5a9d2c]
 /usr/bin/python3() [0x50a533]``` 

[martyngigg]

@SilkeSchomann Would you be free to have a look into this?