From e228fbdc5b2d1a3b0c20c97c3b7f6ae6a8898d23 Mon Sep 17 00:00:00 2001
From: Michele Simionato <michele.simionato@gmail.com>
Date: Sat, 14 Oct 2023 08:41:39 +0200
Subject: [PATCH] Skipping useless calculations

---
 openquake/hazardlib/calc/gmf.py | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/openquake/hazardlib/calc/gmf.py b/openquake/hazardlib/calc/gmf.py
index 2ced07e103e8..6116eee8376e 100644
--- a/openquake/hazardlib/calc/gmf.py
+++ b/openquake/hazardlib/calc/gmf.py
@@ -267,35 +267,38 @@ def compute_all(self, max_iml=None,
         rng = numpy.random.default_rng(self.seed)
         data = AccumDict(accum=[])
         for g, (gs, rlzs) in enumerate(self.cmaker.gsims.items()):
+            idxs, = numpy.where(numpy.isin(self.rlz, rlzs))
+            E = len(idxs)
+            if E == 0:  # crucial for performance
+                continue
             with cmon:
-                array = self.compute(gs, rlzs, mean_stds[:, g], rng)  # NME
+                array = self.compute(gs, idxs, mean_stds[:, g], rng)  # NME
             with umon:
                 self.update(data, array, rlzs, mean_stds[:, g], max_iml)
         with umon:
             return self.strip_zeros(data)
 
-    def compute(self, gsim, rlzs, mean_stds, rng):
+    def compute(self, gsim, idxs, mean_stds, rng):
         """
         :param gsim: GSIM used to compute mean_stds
-        :param rlzs: realizations associated to the gsim
+        :param idxs: affected indices
         :param mean_stds: array of shape (4, M, N)
         :param rng: random number generator for the rupture
         :returns: a 32 bit array of shape (N, M, E)
         """
         # sets self.eps
         M = len(self.imts)
-        mask = numpy.isin(self.rlz, rlzs)
-        E = mask.sum()
+        E = len(idxs)
         result = numpy.zeros(
             (len(self.imts), len(self.ctx.sids), E), F32)
         ccdist = self.cross_correl.distribution
         # build arrays of random numbers of shape (M, N, E) and (M, E)
         intra_eps = [ccdist.rvs((self.N, E), rng) for _ in range(M)]
-        self.eps[mask] = self.cross_correl.get_inter_eps(self.imts, E, rng).T
+        self.eps[idxs] = self.cross_correl.get_inter_eps(self.imts, E, rng).T
         for m, imt in enumerate(self.imts):
             try:
                 result[m] = self._compute(
-                    mean_stds[:, m], m, imt, gsim, intra_eps[m], mask)
+                    mean_stds[:, m], m, imt, gsim, intra_eps[m], idxs)
             except Exception as exc:
                 raise RuntimeError(
                     '(%s, %s, source_id=%r) %s: %s' %
@@ -307,7 +310,7 @@ def compute(self, gsim, rlzs, mean_stds, rng):
                 self.ctx.ampcode, result, self.imts, self.seed)
         return result.transpose(1, 0, 2)
 
-    def _compute(self, mean_stds, m, imt, gsim, intra_eps, mask):
+    def _compute(self, mean_stds, m, imt, gsim, intra_eps, idxs):
         # sets self.sig
         im = imt.string
         if self.cmaker.truncation_level <= 1E-9:
@@ -329,7 +332,7 @@ def _compute(self, mean_stds, m, imt, gsim, intra_eps, mask):
 
             mean, sig, _, _ = mean_stds
             gmf = exp(mean[:, None] + sig[:, None] * intra_eps, im!='MMI')
-            self.sig[mask, m] = numpy.nan
+            self.sig[idxs, m] = numpy.nan
         else:
             mean, sig, tau, phi = mean_stds
             # the [:, None] is used to implement multiplication by row;
@@ -344,10 +347,10 @@ def _compute(self, mean_stds, m, imt, gsim, intra_eps, mask):
                 if len(intra_res.shape) == 1:  # a vector
                     intra_res = intra_res[:, None]
 
-            inter_res = tau[:, None] * self.eps[mask, m]
+            inter_res = tau[:, None] * self.eps[idxs, m]
             # shape (N, 1) * E => (N, E)
             gmf = exp(mean[:, None] + intra_res + inter_res, im!='MMI')
-            self.sig[mask, m] = tau.max()  # from shape (N, 1) => scalar
+            self.sig[idxs, m] = tau.max()  # from shape (N, 1) => scalar
         return gmf  # shapes (N, E)