From 6c892e4d2362f2433bca97a745467fad8a2a3ea9 Mon Sep 17 00:00:00 2001
From: Michael Clerx <michael.clerx@nottingham.ac.uk>
Date: Wed, 11 Aug 2021 03:14:46 +0100
Subject: [PATCH] Added set_hyperparameters method for PopulationMCMC. Closes
 #1327.

---
 pints/_mcmc/_population.py          | 26 ++++++++++++++++++++++++++
 pints/tests/test_mcmc_population.py | 22 ++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/pints/_mcmc/_population.py b/pints/_mcmc/_population.py
index b0183a2b4e..c203315374 100644
--- a/pints/_mcmc/_population.py
+++ b/pints/_mcmc/_population.py
@@ -337,3 +337,29 @@ def temperature_schedule(self):
         distribution is ``p(theta|data) ^ (1 - T)``.
         """
         return self._schedule
+
+    def n_hyper_parameters(self):
+        """ See :meth:`TunableMethod.n_hyper_parameters()`. """
+        return 1
+
+    def set_hyper_parameters(self, x):
+        """
+        The hyper-parameter vector is ``[n_temperatures]``, where
+        ``n_temperatures`` is an integer that will be passed to
+        :meth:`set_temperature_schedule`.
+
+        Note that, since the hyper-parameter vector should be 1d (without
+        nesting), setting an explicit temperature schedule is not supported via
+        the hyper-parameter interface.
+
+        See :meth:`TunableMethod.set_hyper_parameters()`.
+        """
+        try:
+            n_temperatures = int(x[0])
+        except TypeError:
+            raise ValueError(
+                'First hyper-parameter must be (convertible to) an integer'
+                ' (setting an explicit schedule is not supported through the'
+                ' hyper-parameter interface).')
+
+        self.set_temperature_schedule(n_temperatures)
diff --git a/pints/tests/test_mcmc_population.py b/pints/tests/test_mcmc_population.py
index a1e9593bdd..6709f751cb 100755
--- a/pints/tests/test_mcmc_population.py
+++ b/pints/tests/test_mcmc_population.py
@@ -126,6 +126,28 @@ def test_logging(self):
         self.assertIn(' j    ', text)
         self.assertIn(' Ex. ', text)
 
+    def test_hyperparameters(self):
+
+        # Create mcmc
+        mcmc = pints.PopulationMCMC(self.real_parameters)
+
+        # Test setting with an int
+        mcmc.set_temperature_schedule(7)
+        x = mcmc.temperature_schedule()
+        self.assertEqual(len(x), 7)
+        mcmc.set_temperature_schedule(8)
+        self.assertEqual(len(mcmc.temperature_schedule()), 8)
+        mcmc.set_hyper_parameters([7])
+        y = mcmc.temperature_schedule()
+        self.assertEqual(len(y), 7)
+        self.assertTrue(np.all(x == y))
+
+        # Test setting with a list
+        mcmc.set_temperature_schedule(x)
+        self.assertRaisesRegex(
+            ValueError, 'First hyper-parameter',
+            mcmc.set_hyper_parameters, [x])
+
 
 if __name__ == '__main__':
     unittest.main()