Merge pull request #4977 from argriffing/block-diag-dtype

MAINT: more careful dtype treatment in block diagonal matrix construction

scipy/linalg/special_matrices.py

@@ -531,7 +531,8 @@ def block_diag(*arrs):
                          "greater than 2: %s" % bad_args)
 
     shapes = np.array([a.shape if a.size > 0 else [0, 0] for a in arrs])
-    out = np.zeros(np.sum(shapes, axis=0), dtype=arrs[0].dtype)
+    out_dtype = np.find_common_type([arr.dtype for arr in arrs], [])
+    out = np.zeros(np.sum(shapes, axis=0), dtype=out_dtype)
 
     r, c = 0, 0
     for i, (rr, cc) in enumerate(shapes):

scipy/linalg/tests/test_special_matrices.py

@@ -244,6 +244,11 @@ def test_dtype(self):
         x = block_diag([[True]])
         assert_equal(x.dtype, bool)
 
+    def test_mixed_dtypes(self):
+        actual = block_diag([[1]], [[1j]])
+        desired = np.array([[1, 0], [0, 1j]])
+        assert_array_equal(actual, desired)
+
     def test_scalar_and_1d_args(self):
         a = block_diag(1)
         assert_equal(a.shape, (1,1))