move interval quality check into refine()

1 files changed, 18 insertions, 13 deletions

diff --git a/vquad/core.py b/vquad/core.py
index 7435334..f6baedb 100644
--- a/vquad/core.py
+++ b/vquad/core.py
@@ -159,14 +159,26 @@ class Vquad:
         return children
 
     def refine(self, ival):
-        """Increase degree of interval."""
+        """Increase degree of interval.
+
+        Returns True if the refined interval is OK, and False if it is
+        borderline and should not be refined/split further.  This
+        happens when neigboring points can be only barely resolved by
+        floating point numbers, or when the estimated relative error is
+        already at the limit of numerical accuracy and cannot be reduced
+        further.
+        """
         ival.level += 1
         points = ival.points()
         vals = np.empty(points.shape)
         vals[0::2] = ival.vals
         vals[1::2] = self.f(points[1::2])
         ival.interpolate(vals, ival.coeffs)
-        return points
+
+        return (points[1] - points[0] > points[0] * min_sep
+                and points[-1] - points[-2] > points[-2] * min_sep
+                and ival.err > (abs(ival.igral)
+                                * eps * tbls.V_cond_nums[ival.level]))
 
     def improve(self):
         ival = self.ivals[-1]
@@ -174,21 +186,14 @@ class Vquad:
         if ival.level == max_level:
             split = True
         else:
-            points = self.refine(ival)
-            split = ival.unreliable_err
-
-            if (points[1] - points[0] < points[0] * min_sep
-                or points[-1] - points[-2] < points[-2] * min_sep
-                or ival.err < (abs(ival.igral)
-                               * eps * tbls.V_cond_nums[ival.level])):
-                # Remove the interval (while remembering the excess integral
-                # and error), since it is either too narrow, or the estimated
-                # relative error is already at the limit of numerical accuracy
-                # and cannot be reduced further.
+            if not self.refine(ival):
+                # Remove the interval but remember the excess integral and
+                # error.
                 self.err_excess += ival.err
                 self.igral_excess += ival.igral
                 self.attic.append(self.ivals.pop())
                 return
+            split = ival.unreliable_err
 
         if split:
             # Replace current interval by its children.