From b46213546a33e8697ea814d2a3cbd4bb3b3f7c6f Mon Sep 17 00:00:00 2001
From: Max <max.lindqvist@ipp.mpg.de>
Date: Tue, 1 Oct 2024 16:20:28 +0200
Subject: [PATCH] Set imat = np.ones((1, 1), dtype=float) if self.greville.size
 == 1

---
 psydac/fem/splines.py | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/psydac/fem/splines.py b/psydac/fem/splines.py
index 11ebbc1f2..8f2737d45 100644
--- a/psydac/fem/splines.py
+++ b/psydac/fem/splines.py
@@ -171,14 +171,17 @@ def init_interpolation( self, dtype=float ):
         Greville points.
 
         """
-        imat = collocation_matrix(
-            knots    = self.knots,
-            degree   = self.degree,
-            periodic = self.periodic,
-            normalization = self.basis,
-            xgrid    = self.greville,
-            multiplicity = self.multiplicity
-        )
+        if self.greville.size == 1:
+            imat = np.ones((1, 1), dtype=float)
+        else:
+            imat = collocation_matrix(
+                knots    = self.knots,
+                degree   = self.degree,
+                periodic = self.periodic,
+                normalization = self.basis,
+                xgrid    = self.greville,
+                multiplicity = self.multiplicity
+            )
 
         if self.periodic:
             # Convert to CSC format and compute sparse LU decomposition