docstring

Author: pbrubeck

FIAT/hu_lin_zhang.py

@@ -105,6 +105,8 @@ class HuLinZhang(finite_element.CiarletElement):
     """
     HLZ^2(k) is the space of trace-free polynomials of degree k with
     continuous normal-tangential components.
+
+    Reference: https://arxiv.org/abs/2311.15482
     """
     def __init__(self, ref_el, degree=1):
         poly_set = HLZSpace(ref_el, degree)