"""
Create unions or intersections of events
========================================
"""

# %%
# Abstract
# --------
#
# This example illustrates system events, which are defined as unions or intersections of other events.
# We will show how to estimate their probability both with Monte-Carlo sampling
# (using the class :class:`~openturns.ProbabilitySimulationAlgorithm`)
# and with a first order approximation (using the class :class:`~openturns.SystemFORM`).
#
import openturns as ot
import openturns.viewer as otv

# %%
# **Intersection**
#
# The event defined as the intersection of several events is realized when all sub-events occurs:
#
# .. math::
#    E_{sys} = \bigcap_{i=1}^N E_i
#
# **Union**
#
# The event defined as the union of several events is realized when at least one sub-event occurs:
#
# .. math::
#    E_{sys} = \bigcup_{i=1}^N E_i
#


# %%
# We consider a bivariate standard Gaussian random vector `X = (X_1, X_2)`.
dim = 2
distribution = ot.Normal(dim)
X = ot.RandomVector(distribution)


# %%
# We want to estimate the probability given by
#
# .. math::
#
#    P  = \mathbb{E}[\mathbf{1}_{\mathrm{Event}}(X_1, X_2)].
#
# We now build several events using intersections and unions.
#

# %%
# We consider three functions `f1`, `f2` and `f3` :
f1 = ot.SymbolicFunction(["x0", "x1"], ["x0"])
f2 = ot.SymbolicFunction(["x0", "x1"], ["x1"])
f3 = ot.SymbolicFunction(["x0", "x1"], ["x0+x1"])

# %%
# We build :class:`~openturns.CompositeRandomVector` from these functions and the initial distribution.
Y1 = ot.CompositeRandomVector(f1, X)
Y2 = ot.CompositeRandomVector(f2, X)
Y3 = ot.CompositeRandomVector(f3, X)

# %%
# We define three basic events :math:`E_1=\{(x_0,x_1)~:~x_0 < 0 \}`, :math:`E_2=\{(x_0,x_1)~:~x_1 > 0 \}` and :math:`E_3=\{(x_0,x_1)~:~x_0+x_1>0 \}`.
e1 = ot.ThresholdEvent(Y1, ot.Less(), 0.0)
e2 = ot.ThresholdEvent(Y2, ot.Greater(), 0.0)
e3 = ot.ThresholdEvent(Y3, ot.Greater(), 0.0)

# %%
# The restriction of the domain :math:`E_1` to :math:`[-4,4] \times [-4, 4]` is the grey area.
myGraph = ot.Graph(r"Representation of the event $E_1$", r"$x_1$", r"$x_2$", True, "")
data = [[-4, -4], [0, -4], [0, 4], [-4, 4]]
myPolygon = ot.Polygon(data)
myPolygon.setColor("grey")
myPolygon.setEdgeColor("black")
myGraph.add(myPolygon)
view = otv.View(myGraph)
axes = view.getAxes()
_ = axes[0].set_xlim(-4.0, 4.0)
_ = axes[0].set_ylim(-4.0, 4.0)


# %%
# The restriction of the domain :math:`E_2` to :math:`[-4,4] \times [-4, 4]` is the grey area.
myGraph = ot.Graph(r"Representation of the event $E_2$", r"$x_1$", r"$x_2$", True, "")
data = [[-4, 0], [4, 0], [4, 4], [-4, 4]]
myPolygon = ot.Polygon(data)
myPolygon.setColor("grey")
myPolygon.setEdgeColor("black")
myGraph.add(myPolygon)
view = otv.View(myGraph)
axes = view.getAxes()
_ = axes[0].set_xlim(-4.0, 4.0)
_ = axes[0].set_ylim(-4.0, 4.0)

# %%
# The restriction of the domain :math:`E_3` to :math:`[-4,4] \times [-4, 4]` is the grey area.
myGraph = ot.Graph(r"Representation of the event $E_3$", r"$x_1$", r"$x_2$", True, "")
data = [[-4, 4], [4, -4], [4, 4]]
myPolygon = ot.Polygon(data)
myPolygon.setColor("grey")
myPolygon.setEdgeColor("black")
myGraph.add(myPolygon)
view = otv.View(myGraph)
axes = view.getAxes()
_ = axes[0].set_xlim(-4.0, 4.0)
_ = axes[0].set_ylim(-4.0, 4.0)

# %%
# We can define the intersection :math:`E_4 = E_1 \bigcap E_2`: that is the upper left quadrant.
e4 = ot.IntersectionEvent([e1, e2])

# %%
# The restriction of the domain :math:`E_4` to :math:`[-4,4] \times [-4, 4]` is the grey area.
myGraph = ot.Graph(
    r"Representation of the event $E_4  = E_1 \bigcap E_2$",
    r"$x_1$",
    r"$x_2$",
    True,
    "",
)
data = [[-4, 0], [0, 0], [0, 4], [-4, 4]]
myPolygon = ot.Polygon(data)
myPolygon.setColor("grey")
myPolygon.setEdgeColor("black")
myGraph.add(myPolygon)
view = otv.View(myGraph)
axes = view.getAxes()
_ = axes[0].set_xlim(-4.0, 4.0)
_ = axes[0].set_ylim(-4.0, 4.0)

# %%
# The probability of that event is :math:`P_{E_4} = 1/4`. A basic estimator is:
print("Probability of e4 : %.4f" % e4.getSample(10000).computeMean()[0])

# %%
# We define the union :math:`E_5 = E1 \bigcup E_2`. It is the whole plan without the lower right quadrant.
e5 = ot.UnionEvent([e1, e2])

# %%
# The restriction of the domain :math:`E_5` to :math:`[-4,4] \times [-4, 4]` is the grey area.
myGraph = ot.Graph(
    r"Representation of the event $E_5  = E_1 \bigcup E_2$",
    r"$x_1$",
    r"$x_2$",
    True,
    "",
)
data = [[-4, -4], [0, -4], [0, 0], [4, 0], [4, 4], [-4, 4]]
myPolygon = ot.Polygon(data)
myPolygon.setColor("grey")
myPolygon.setEdgeColor("black")
myGraph.add(myPolygon)
view = otv.View(myGraph)
axes = view.getAxes()
_ = axes[0].set_xlim(-4.0, 4.0)
_ = axes[0].set_ylim(-4.0, 4.0)

# %%
# The probability of that event is :math:`P_{E_5} = 3/4`. A basic estimator is:
print("Probability of e5 : %.4f" % e5.getSample(10000).computeMean()[0])

# %%
# It supports recursion. Let's define :math:`E_6 = E_1 \bigcup (E_2 \bigcap E_3)`.
e6 = ot.UnionEvent([e1, ot.IntersectionEvent([e2, e3])])


# %%
# First we draw the domain :math:`E_6 = E_1 \bigcup (E_2 \bigcap E_3)` :
myGraph = ot.Graph(
    r"Representation of the event $E_2 \bigcap E_3 $", r"$x_1$", r"$x_2$", True, ""
)
data = [[-4, 4], [0, 0], [4, 0], [4, 4]]
myPolygon = ot.Polygon(data)
myPolygon.setColor("grey")
myPolygon.setEdgeColor("black")
myGraph.add(myPolygon)
view = otv.View(myGraph)
axes = view.getAxes()
_ = axes[0].set_xlim(-4.0, 4.0)
_ = axes[0].set_ylim(-4.0, 4.0)

# %%
# From the previous figures we easily deduce that the event :math:`E_6 = E_1 \bigcup (E_2 \bigcap E_3)`
# is the event :math:`E_5` and the probability is :math:`P_{E_6} = 3/4`. We can use a basic estimator and get :
print("Probability of e6 : %.4f" % e6.getSample(10000).computeMean()[0])


# %%
# Usage with a Monte-Carlo algorithm
# ----------------------------------
#
# Of course, we can use simulation algorithms with this kind of events.

# %%
# We set up a :class:`~openturns.MonteCarloExperiment` and a :class:`~openturns.ProbabilitySimulationAlgorithm` on the event :math:`E_6`.
experiment = ot.MonteCarloExperiment()
algo = ot.ProbabilitySimulationAlgorithm(e6, experiment)
algo.setMaximumOuterSampling(2500)
algo.setBlockSize(4)
algo.setMaximumCoefficientOfVariation(-1.0)
algo.run()

# %%
# We retrieve the results and display the approximate probability and a confidence interval :
result = algo.getResult()
prb = result.getProbabilityEstimate()
print("Probability of e6 through MC : %.4f" % prb)
cl = result.getConfidenceLength()
print("Confidence interval MC : [%.4f, %.4f]" % (prb - 0.5 * cl, prb + 0.5 * cl))


# %%
# Usage with SystemFORM
# ---------------------
#
# The :class:`~openturns.SystemFORM` class implements an approximation method suitable for system events.
# The event must be in its disjunctive normal form (union of intersections, or a single intersection).

# %%
# For system events, we always have to use the same root cause (input distribution). Here we use input variables with a
# normal distribution specified by its mean, standard deviation and correlation matrix.
#
dim = 5
mean = [200.0] * dim
mean[-1] = 60
mean[-2] = 60
sigma = [30.0] * dim
sigma[-1] = 15.0
R = ot.CorrelationMatrix(dim)
for i in range(dim):
    for j in range(i):
        R[i, j] = 0.5
dist = ot.Normal(mean, sigma, R)


# %%
# As usual we create a :class:`~openturns.RandomVector` out of the input distribution.
X = ot.RandomVector(dist)

# %%
# We define the leaf events thanks to :class:`~openturns.SymbolicFunction`.
inputs = ["M1", "M2", "M3", "M4", "M5"]
e0 = ot.ThresholdEvent(
    ot.CompositeRandomVector(ot.SymbolicFunction(inputs, ["M1-M2+M4"]), X),
    ot.Less(),
    0.0,
)
e1 = ot.ThresholdEvent(
    ot.CompositeRandomVector(ot.SymbolicFunction(inputs, ["M2+2*M3-M4"]), X),
    ot.Less(),
    0.0,
)
e2 = ot.ThresholdEvent(
    ot.CompositeRandomVector(ot.SymbolicFunction(inputs, ["2*M3-2*M4-M5"]), X),
    ot.Less(),
    0.0,
)
e3 = ot.ThresholdEvent(
    ot.CompositeRandomVector(ot.SymbolicFunction(inputs, ["-(M1+M2+M4+M5-5*10.0)"]), X),
    ot.Less(),
    0.0,
)
e4 = ot.ThresholdEvent(
    ot.CompositeRandomVector(ot.SymbolicFunction(inputs, ["-(M2+2*M3+M4-5*40.0)"]), X),
    ot.Less(),
    0.0,
)

# %%
# We consider a system event in disjunctive normal form (union of intersections):
event = ot.UnionEvent(
    [ot.IntersectionEvent([e0, e3, e4]), ot.IntersectionEvent([e2, e3, e4])]
)

# %%
# We can estimate the probability of the event with basic sampling.
print("Probability of the event : %.4f" % event.getSample(10000).computeMean()[0])

# %%
# We can also run a :class:`~openturns.SystemFORM` algorithm to estimate the probability differently.

# %%
# We first set up a solver to find the design point.
solver = ot.AbdoRackwitz()
solver.setMaximumIterationNumber(1000)
solver.setMaximumAbsoluteError(1.0e-3)
solver.setMaximumRelativeError(1.0e-3)
solver.setMaximumResidualError(1.0e-3)
solver.setMaximumConstraintError(1.0e-3)

# %%
# We build the :class:`~openturns.SystemFORM` algorithm from the solver, the event and a starting point (here the mean) and then run the algorithm.
solver.setStartingPoint(mean)
algo = ot.SystemFORM(solver, event)
algo.run()

# %%
# We store the result and display the probability.
result = algo.getResult()
prbSystemFORM = result.getEventProbability()
print("Probability of the event (SystemFORM) : %.4f" % prbSystemFORM)

# %%
# Display all figures
otv.View.ShowAll()
