Allow passing a maximum degree quadrature to a measure

docs/source/quadrature.rst

@@ -15,9 +15,9 @@ this estimate might be quite large, and a warning like this one will be raised:
 
    tsfc:WARNING Estimated quadrature degree 13 more than tenfold greater than any argument/coefficient degree (max 1)
 
-For integrals with very complicated nonlinearities, the estimated quadrature
-degree might be in the hundreds or thousands, rendering the integration
-prohibitively expensive, or leading to segfaults.
+For integrals with very complicated or non-polynomial nonlinearities, the
+estimated quadrature degree might be in the hundreds or thousands, rendering
+the integration prohibitively expensive, or leading to segfaults.
 
 Specifying the quadrature rule in the variational formulation
 -------------------------------------------------------------
@@ -46,6 +46,17 @@ In the example above, only the integrals with unspecified quadrature degree
 will be computed on a quadrature rule that exactly integrates polynomials of
 the degree set in ``form_compiler_parameters``.
 
+Rather than enforcing a specific quadrature degree, it is also possible to set
+a maximum allowable degree which will only be used if UFL estimates a larger
+degree. This can be set for all integrals by adding the ``"max_quadrature_degree"``
+entry to the ``form_compiler_parameters``.
+A maximum allowable quadrature degree can be set for a particular integral by
+adding the ``"max_quadrature_degree"`` entry to the ``metadata`` of the ``Measure``:
+
+.. code-block:: python3
+
+   inner(sin(u)**4, v) * dx(metadata={"max_quadrature_degree": 4})
+
 Another way to specify the quadrature rule is through the ``scheme`` keyword. This could be
 either a :py:class:`~finat.quadrature.QuadratureRule`, or a string. Supported string values
 are ``"default"``, ``"canonical"``, and ``"KMV"``. For more details see

tsfc/kernel_interface/common.py

@@ -320,11 +320,20 @@ def set_quad_rule(params, cell, integral_type, functions):
                         if e.family() in {"Quadrature", "Boundary Quadrature"})
         if len(quad_data) == 0:
             quadrature_degree = params["estimated_polynomial_degree"]
-            if all((asarray(quadrature_degree) > 10 * asarray(e.degree())).all() for e in elements):
-                logger.warning("Estimated quadrature degree %s more "
-                               "than tenfold greater than any "
-                               "argument/coefficient degree (max %s)",
-                               quadrature_degree, max_degree([e.degree() for e in elements]))
+            if "max_quadrature_degree" in params:
+                max_allowed_degree = params["max_quadrature_degree"]
+                if quadrature_degree > max_allowed_degree:
+                    logger.info("Estimated quadrature degree %s greater "
+                                "than maximum allowed degree %s. "
+                                "Using maximum degree %s instead.",
+                                quadrature_degree, max_allowed_degree, max_allowed_degree)
+                    quadrature_degree = max_allowed_degree
+            else:
+                if all((asarray(quadrature_degree) > 10 * asarray(e.degree())).all() for e in elements):
+                    logger.warning("Estimated quadrature degree %s more "
+                                   "than tenfold greater than any "
+                                   "argument/coefficient degree (max %s)",
+                                   quadrature_degree, max_degree([e.degree() for e in elements]))
         else:
             try:
                 (quadrature_degree, quad_rule), = quad_data