Fix Chain.form_matrix to work with scipy 1.12 (#2922)

openmc/deplete/chain.py

@@ -597,9 +597,12 @@ class Chain:
         --------
         :meth:`get_default_fission_yields`
         """
-        matrix = defaultdict(float)
         reactions = set()
 
+        # Use DOK matrix as intermediate representation for matrix
+        n = len(self)
+        matrix = sp.dok_matrix((n, n))
+
         if fission_yields is None:
             fission_yields = self.get_default_fission_yields()
 
@@ -674,11 +677,8 @@ class Chain:
                 # Clear set of reactions
                 reactions.clear()
 
-        # Use DOK matrix as intermediate representation, then convert to CSC and return
-        n = len(self)
-        matrix_dok = sp.dok_matrix((n, n))
-        dict.update(matrix_dok, matrix)
-        return matrix_dok.tocsc()
+        # Return CSC representation instead of DOK
+        return matrix.tocsc()
 
     def form_rr_term(self, tr_rates, mats):
         """Function to form the transfer rate term matrices.
@@ -711,7 +711,9 @@ class Chain:
             Sparse matrix representing transfer term.
 
         """
-        matrix = defaultdict(float)
+        # Use DOK as intermediate representation
+        n = len(self)
+        matrix = sp.dok_matrix((n, n))
 
         for i, nuc in enumerate(self.nuclides):
             elm = re.split(r'\d+', nuc.name)[0]
@@ -737,10 +739,9 @@ class Chain:
                 else:
                     matrix[i, i] = 0.0
             #Nothing else is allowed
-        n = len(self)
-        matrix_dok = sp.dok_matrix((n, n))
-        dict.update(matrix_dok, matrix)
-        return matrix_dok.tocsc()
+
+        # Return CSC instead of DOK
+        return matrix.tocsc()
 
     def get_branch_ratios(self, reaction="(n,gamma)"):
         """Return a dictionary with reaction branching ratios

setup.py

@@ -64,7 +64,7 @@ kwargs = {
     # Dependencies
     'python_requires': '>=3.7',
     'install_requires': [
-        'numpy>=1.9', 'h5py', 'scipy<1.12', 'ipython', 'matplotlib',
+        'numpy>=1.9', 'h5py', 'scipy', 'ipython', 'matplotlib',
         'pandas', 'lxml', 'uncertainties'
     ],
     'extras_require': {