AiiDAEnsemble: add missing self.init()

[bastonero]

Fixes #334

The version update v1.4.1 missed to add the new init function to the compute_ensemble method of the auxiliary class AiiDAEnsemble. The simple fix makes the calculation using this class comparable to the traditional Ensemble class.

[diegomartinez2]

Hi, I do not see the "init" function in 'compute_ensemble'. Why not use a __init__ method to automatically initialize the object?, that way you don't need to call a self.init().

[bastonero]

Hi @diegomartinez2 , thanks for reviewing the code. As you cans see, the function is called here, at the end of the compute_ensemble method. This mimics the behaviour of the Ensemble class. The AiiDAEnsemble in facts subclasses the Ensemble one, hence it is provided with this method. This function (def init()), according to documentation, must be called after the calculation of the ensemble, not to initialize the object itself.

[mesonepigreco]

@diegomartinez2
The new version has a different def init(self) that initializes the variables for the calculation of the Gradient in fourier space.
This initialization perform the fourier transform of the displacements and the forces. In this case, it is necessary to have already generated both the displacements and computed the forces before doing the initialization of the fourier calculation.
This is the reason why it is required to run self.init() (which is not the init used to create the ensemble) after the forces and displacements of the ensemble have been computed.

We have this in Ensemble.compute_ensemble

if timer:
      timer.execute_timed_function(self.init)
else:
      self.init()

Since the AiiDA Ensemble is overwriting the compute_ensemble, by missing the self.init there prevents the correct initialization of the fourier gradient calculation (and consequently the wrong minimization).

[mesonepigreco]

We could use this patch for 1.4.2 since a long time is probably required for 1.5, and we have tons of small fixes to tdscha and cell constructor that have occurred since the last release.

[mesonepigreco]

The edit is minimal and the testsuite is passing. It should be merged without problems