Change default solver to scipy's spsolve if pypardiso is not found
Currently, the default solver is `pypardiso`, which relies on MKL, and installing MKL using `pip` seems to be not so straightforward.
diff --git a/openpnm/algorithms/GenericTransport.py b/openpnm/algorithms/GenericTransport.py
index ef8440c11..adea405ea 100644
--- a/openpnm/algorithms/GenericTransport.py
+++ b/openpnm/algorithms/GenericTransport.py
@@ -669,11 +669,23 @@ class GenericTransport(GenericAlgorithm):
                 return x
         # PyPardiso
         elif self.settings['solver_family'] == 'pypardiso':
+            try:
+                import pypardiso
+            except ModuleNotFoundError:
+                if self.Np <= 8000:
+                    logger.critical("Pardiso not found, reverting to much "
+                                    + "slower spsolve.  Install pardiso with: "
+                                    + "conda install -c conda-forge pardiso4py")
+                    self.settings['solver_family'] = 'scipy'
+                    return self._get_solver()
+                else:
+                    raise Exception("Pardiso not found. Install it with: "
+                                    + "conda install -c conda-forge pardiso4py")
+
             def solver(A, b, **kwargs):
                 r"""
                 Wrapper method for PyPardiso sparse linear solver.
                 """
-                import pypardiso
                 x = pypardiso.spsolve(A=A, b=b)
                 return x
         else:
['openpnm/algorithms/GenericTransport.py']