Bug in processing Jacobian

[talassio]

Providing the Jacobian with option options%fortran_jacobian = .True. OR providing Jacobian transpose with option options%fortran_jacobian = .False. should be (numerically) equivalent.

Minimal example provided wtih lanczos3.f90, currently only for some combinations of options%... the behaviour is as expected, for the others combinations diffs are present in solution paths.

[talassio]

Further comments to resolve the issue:

• mult_j and mult_Jt should not have options to be optional, forcing to discern between using the Jacobian or Jacobian transpose (Gradient). This will require to update model=4 evaltensor_* callbacks which currently do not handle the case of Jacobian transpose.

• evaltensor_f make call to mult_j regardless of options%fortran_jacobian. It should be updated so to check the case of the options%fortran_jacobian and either call mult_j with options or mult_j/mult_jt depending on the option value.

• evaltensor_j in all three loops assumes J is the Jacobian, this needs to be updated to take into account the value of options%fortran_jacobian.

• solve_LLS is also assuming J is provided in column major format

The signature to mult_j and mult_jt could be changed to accept logical fortran_jacobian instead of nlls_options options, this would simplify the passing of the value into the evaltensor_*callbacks. Furthermore, tensor_params_type could be extended to include a new member logical fortran_jacobian to be passed onto mult_j.