"""
Apply a Box-Cox transformation to a Field
=========================================
"""
# %%
#
# The objective of this Use Case is to estimate a Box Cox transformation
# from a field which all values are positive (eventually after a shift
# to satisfy the positiveness) and to apply it on the field.
# The object *BoxCoxFactory* enables to create a factory of
# Box Cox transformation.
# Then, we estimate the Box Cox transformation
# :math:`h_{\underline{\lambda}}` from the initial field values
# :math:`(\underline{x}_0, \dots, \underline{x}_{N-1})` thanks to the method
# *build* of the object *BoxCoxFactory*, which produces an object of
# type *BoxCoxTransform*.
# If the field values :math:`(\underline{x}_0, \dots, \underline{x}_{N-1})` have
# some negative values, it is possible to translate the values with
# respect a given shift :math:`\underline{\alpha}` which has to be mentioned
# either at the creation of the object *BoxCoxFactory* or when using the
# method *build*.
# Then the Box Cox transformation is the composition of
# :math:`h_{\underline{\lambda}}` and this translation.
#
# The object *BoxCoxTransform* enables to:
#
# -  transform the field values
#    :math:`(\underline{x}_{0}, \dots,\underline{x}_{N-1})` of dimension :math:`d`
#    into the values :math:`(\underline{y}_{0}, \dots, \underline{y}_{N-1})` with
#    stabilized variance, such that for each vertex :math:`\underline{t}_i` we
#    have:
#
#    :math:`\underline{y}_{i} = h_{\underline{\lambda}}(\underline{x}_{i})`
#
#     or
#
#    :math:`\underline{y}_{i} = h_{\underline{\lambda}}(\underline{x}_{i} + \underline{\alpha})`
#
#    thanks to the operand *()*. The field based on the values
#    :math:`\underline{y}_{i}` shares the same mesh than the initial field.
#
# -  create the inverse Box Cox transformation such that :
#
#    :math:`\underline{x}_{i}= h^{-1}_{\underline{\lambda}}(\underline{y}_{i})`
#
#     or
#
#    :math:`\underline{x}_{i} = h^{-1}_{\underline{\lambda}}(\underline{y}_{i}) - \underline{\alpha}`
#
#    thanks to the method *getInverse()* which produces an object of type
#    *InverseBoxCoxTransform* that can be evaluated on a field.
#    The new field based shares the same mesh than the initial field.
#

# %%
from __future__ import print_function
import openturns as ot
import openturns.viewer as viewer
from matplotlib import pylab as plt
ot.Log.Show(ot.Log.NONE)

# %%
# Define a process
myIndices= ot.Indices([10,5])
myMesher =ot.IntervalMesher(myIndices)
myInterval = ot.Interval([0.0, 0.0], [2.0, 1.0])
myMesh = myMesher.build(myInterval)
amplitude = [1.0]
scale = [0.2, 0.2]
myCovModel = ot.ExponentialModel(scale, amplitude)
myXproc = ot.GaussianProcess(myCovModel, myMesh)
g = ot.SymbolicFunction(['x1'],  ['exp(x1)'])
myDynTransform = ot.ValueFunction(g, myMesh)
myXtProcess = ot.CompositeProcess(myDynTransform, myXproc)

# %%
# Draw a field
field = myXtProcess.getRealization()
graph = field.drawMarginal(0)
view = viewer.View(graph)

# %%
# Draw values
marginal = ot.HistogramFactory().build(field.getValues())
graph = marginal.drawPDF()
view = viewer.View(graph)

# %%
# Build the transformed field through Box-Cox
myModelTransform = ot.BoxCoxFactory().build(field)
myStabilizedField = myModelTransform(field)

# %%
# Draw values
marginal = ot.HistogramFactory().build(myStabilizedField.getValues())
graph = marginal.drawPDF()
view = viewer.View(graph)
plt.show()
