From 852e49f32aedad4a0b3c5ddb33684a59442a6b87 Mon Sep 17 00:00:00 2001
From: Antony Lee <anntzer.lee@gmail.com>
Date: Sun, 1 Jan 2023 20:58:46 +0100
Subject: [PATCH] Use np.linalg.slogdet where possible.

---
 lib/hmmlearn/_kl_divergence.py | 14 ++++++++------
 lib/hmmlearn/_utils.py         | 11 +++++++++++
 lib/hmmlearn/vhmm.py           |  5 ++---
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/lib/hmmlearn/_kl_divergence.py b/lib/hmmlearn/_kl_divergence.py
index fa78c703..5fbdb7cd 100644
--- a/lib/hmmlearn/_kl_divergence.py
+++ b/lib/hmmlearn/_kl_divergence.py
@@ -7,6 +7,8 @@
 import numpy as np
 from scipy.special import gammaln, digamma
 
+from . import _utils
+
 
 def kl_dirichlet(q, p):
     """
@@ -54,10 +56,10 @@ def kl_multivariate_normal_distribution(mean_q, covar_q, mean_p, covar_p):
     D = mean_q.shape[0]
 
     # These correspond to the four terms in the ~wpenny paper documented above
-    return (0.5 * np.log(np.linalg.det(covar_p) / np.linalg.det(covar_q))
-            + 0.5 * np.trace(precision_p @ covar_q)
-            + 0.5 * mean_diff @ precision_p @ mean_diff
-            - D/2)
+    return .5 * (_utils.logdet(covar_p) - _utils.logdet(covar_q)
+                 + np.trace(precision_p @ covar_q)
+                 + mean_diff @ precision_p @ mean_diff
+                 - D)
 
 
 def kl_gamma_distribution(b_q, c_q, b_p, c_p):
@@ -104,12 +106,12 @@ def _E(dof, scale):
     r"""
     $L(a, B) = \int \mathcal{Wishart}(\Gamma; a, B) \log |\Gamma| d\Gamma$
     """
-    return (-np.log(np.linalg.det(scale / 2))
+    return (-_utils.logdet(scale / 2)
             + digamma((dof - np.arange(scale.shape[0])) / 2).sum())
 
 
 def _logZ(dof, scale):
     D = scale.shape[0]
     return ((D * (D - 1) / 4) * np.log(np.pi)
-            - dof / 2 * np.log(np.linalg.det(scale / 2))
+            - dof / 2 * _utils.logdet(scale / 2)
             + gammaln((dof - np.arange(scale.shape[0])) / 2).sum())
diff --git a/lib/hmmlearn/_utils.py b/lib/hmmlearn/_utils.py
index 5b2ad8c6..f5456dd6 100644
--- a/lib/hmmlearn/_utils.py
+++ b/lib/hmmlearn/_utils.py
@@ -1,9 +1,20 @@
 """Private utilities."""
 
+import warnings
+
 import numpy as np
 from sklearn.utils.validation import NotFittedError
 
 
+def logdet(a):
+    sign, logdet = np.linalg.slogdet(a)
+    if (sign < 0).any():
+        warnings.warn("invalid value encountered in log", RuntimeWarning)
+        return np.where(sign < 0, np.nan, logdet)
+    else:
+        return logdet
+
+
 def split_X_lengths(X, lengths):
     if lengths is None:
         return [X]
diff --git a/lib/hmmlearn/vhmm.py b/lib/hmmlearn/vhmm.py
index 42377039..2b4bbe6b 100644
--- a/lib/hmmlearn/vhmm.py
+++ b/lib/hmmlearn/vhmm.py
@@ -648,12 +648,11 @@ def _compute_subnorm_log_likelihood(self, X):
             scale_posterior_ = fill_covars(self.scale_posterior_,
                     self.covariance_type, self.n_components, self.n_features)
         W_k = np.linalg.inv(scale_posterior_)
-        term1 += self.n_features * np.log(2)
-        term1 += np.log(np.linalg.det(W_k))
+        term1 += self.n_features * np.log(2) + _utils.logdet(W_k)
         term1 /= 2
 
         # We ignore the constant that is typically excluded in the literature
-        # term2 = self.n_features * log(2 * M_PI ) / 2
+        # term2 = self.n_features * log(2 * M_PI) / 2
         term2 = 0
         term3 = self.n_features / self.beta_posterior_