Add flag to ignore linearity errors (#142)

Add the flag `ignore_linearity_errors` to the constructors of
`BilinearForm` and `LinearForm`. Such a flag converts the error
of the linearity check into a warning. This is useful because the
linearity check sometimes fails due to small roundoff errors.

Update version to 0.18.2.

---------

Co-authored-by: Yaman Güçlü <[email protected]>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name            = "sympde"
-version         = "0.18.1"
+version         = "0.18.2"
 description     = "Symbolic calculus for partial differential equations (and variational forms)"
 readme          = "README.rst"
 requires-python = ">= 3.8, < 3.12"

sympde/expr/expr.py

@@ -334,7 +334,7 @@ def space(self):
 class LinearForm(BasicForm):
     is_linear = True
 
-    def __new__(cls, arguments, expr, **options):
+    def __new__(cls, arguments, expr, ignore_linearity_errors=False, **options):
 
         # Trivial case: null expression
         if expr == 0:
@@ -349,8 +349,13 @@ def __new__(cls, arguments, expr, **options):
 
         # Check linearity with respect to the given arguments
         if not is_linear_expression(expr, args):
-            msg = 'Expression is not linear w.r.t [{}]'.format(args)
-            raise UnconsistentLinearExpressionError(msg)
+            print(expr)
+            print(args)
+            msg = f'Expression is not linear w.r.t. [{args}]'
+            if ignore_linearity_errors:
+                print(msg)
+            else:
+                raise UnconsistentLinearExpressionError(msg)
 
         # Create new object of type LinearForm
         obj = Basic.__new__(cls, args, expr)
@@ -414,7 +419,7 @@ class BilinearForm(BasicForm):
     is_bilinear = True
     _is_symmetric = None
 
-    def __new__(cls, arguments, expr, **options):
+    def __new__(cls, arguments, expr, ignore_linearity_errors=False, **options):
 
         # Trivial case: null expression
         if expr == 0:
@@ -433,15 +438,20 @@ def __new__(cls, arguments, expr, **options):
 
         # Check linearity with respect to trial functions
         if not is_linear_expression(expr, trial_functions):
-            msg = ' Expression is not linear w.r.t trial functions {}'\
-                    .format(trial_functions)
-            raise UnconsistentLinearExpressionError(msg)
+            msg = f'Expression is not linear w.r.t. trial functions [{trial_functions}]'
+            if ignore_linearity_errors:
+                print(msg)
+            else:
+                raise UnconsistentLinearExpressionError(msg)
+
 
         # Check linearity with respect to test functions
         if not is_linear_expression(expr, test_functions):
-            msg = ' Expression is not linear w.r.t test functions {}'\
-                    .format(test_functions)
-            raise UnconsistentLinearExpressionError(msg)
+            msg = f'Expression is not linear w.r.t. test functions [{test_functions}]'
+            if ignore_linearity_errors:
+                print(msg)
+            else:
+                raise UnconsistentLinearExpressionError(msg)
 
         # Create new object of type BilinearForm
         obj = Basic.__new__(cls, args, expr)