From 47f5bbaaa7beec9c3132b9e4e541701b977dfce0 Mon Sep 17 00:00:00 2001
From: Giordon Stark <kratsg@gmail.com>
Date: Thu, 5 Mar 2020 07:53:22 -0800
Subject: [PATCH] add mixin idea

---
 src/pyhf/infer/mixins.py | 99 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 src/pyhf/infer/mixins.py

diff --git a/src/pyhf/infer/mixins.py b/src/pyhf/infer/mixins.py
new file mode 100644
index 0000000000..408586dfe8
--- /dev/null
+++ b/src/pyhf/infer/mixins.py
@@ -0,0 +1,99 @@
+"""
+Mixins for Hypothesis Testing.
+"""
+from .. import get_backend
+from .test_statistics import qmu
+
+
+class Calculator(object):
+    def __init__(
+        self, data, pdf, init_pars=None, par_bounds=None, qtilde=False, ntoys=2000
+    ):
+        self.data = data
+        self.pdf = pdf
+        self.init_pars = init_pars or pdf.config.suggested_init()
+        self.par_bounds = par_bounds or pdf.config.suggested_bounds()
+        self.qtilde = qtilde
+        self.distribution = None
+
+        # TODO: better names???
+        # for Asymptotics, it is self.sqrtqmuA_v
+        # for Toys, it is signal/bkg qtilde
+        self.something_signal = None
+        self.something_bkg = None
+
+        # toys
+        self.ntoys = ntoys
+
+    def distributions(self, poi_test):
+        if self.something_signal is None or self.something_bkg is None:
+            raise RuntimeError('need to call .teststatistic(poi_test) first')
+
+        if self.distribution is None:
+            raise RuntimeError('need to call this from a mixin\'d class')
+
+        s_plus_b = self.distribution(signal_qtilde)
+        b_only = self.distribution(bkg_qtilde)
+        return s_plus_b, b_only
+
+
+class AsymptoticCalculator(Calculator):
+    def teststatistic(self, poi_test):
+        tensorlib, _ = get_backend()
+        qmu_v = qmu(poi_test, self.data, self.pdf, self.init_pars, self.par_bounds)
+        sqrtqmu_v = tensorlib.sqrt(qmu_v)
+
+        asimov_mu = 0.0
+        asimov_data = generate_asimov_data(
+            asimov_mu, self.data, self.pdf, self.init_pars, self.par_bounds
+        )
+        qmuA_v = qmu(poi_test, asimov_data, self.pdf, self.init_pars, self.par_bounds)
+        self.something_signal = -tensorlib.sqrt(qmuA_v)
+        self.something_bkg = 0.0
+
+        if not self.qtilde:  # qmu
+            teststat = sqrtqmu_v + self.something_signal
+        else:  # qtilde
+
+            def _true_case():
+                teststat = sqrtqmu_v + self.something_signal
+                return teststat
+
+            def _false_case():
+                qmu = tensorlib.power(sqrtqmu_v, 2)
+                qmu_A = tensorlib.power(self.something_signal, 2)
+                teststat = (qmu_A - qmu) / (2 * self.something_signal)
+                return teststat
+
+            teststat = tensorlib.conditional(
+                (sqrtqmu_v < self.something_signal), _true_case, _false_case
+            )
+        return teststat
+
+
+class ToyCalculator(Calculator):
+    def teststatistic(self, poi_test):
+        tensorlib, _ = get_backend()
+        sample_shape = (self.ntoys,)
+
+        signal_pars = [*self.init_pars]
+        signal_pars[self.pdf.config.poi_index] = poi_test
+        signal_pdf = self.pdf.make_pdf(tensorlib.astensor(signal_pars))
+        signal_sample = signal_pdf.sample(sample_shape)
+
+        bkg_pars = [*self.init_pars]
+        bkg_pars[self.pdf.config.poi_index] = 0.0
+        bkg_pdf = self.pdf.make_pdf(tensorlib.astensor(bkg_pars))
+        bkg_sample = bkg_pdf.sample(sample_shape)
+
+        self.qtilde_signal = tensorlib.astensor(
+            qmu(poi_test, sample, self.pdf, signal_pars, self.par_bounds)
+            for sample in signal_sample
+        )
+        self.qtilde_bkg = tensorlib.astensor(
+            qmu(poi_test, sample, self.pdf, bkg_pars, self.par_bounds)
+            for sample in bkg_sample
+        )
+
+        qmu_v = qmu(poi_test, self.data, self.pdf, self.init_pars, self.par_bounds)
+        return qmu_v