Merge branch 'feature/cholmod-error-code' into 'master'

CholmodSolver: Add error code member

See merge request !44

CHANGELOG.md

 # Master (will become release 2.8)
 
-- ...
+- CholmodSolver: Added `errorCode_` member to report errors and warnings during the matrix decomposition
 
 ## Deprecations and removals
 

dune/solvers/solvers/cholmodsolver.hh

@@ -93,7 +93,12 @@ public:
     {
       // the apply() method doesn't like constant values
       auto mutableRhs = *rhs_;
+
+      // setMatrix will decompose the matrix
       solver.setMatrix(*matrix_);
+      // get the error code from Cholmod in case something happened
+      errorCode_ = solver.cholmodCommonObject().status;
+
       solver.apply(*x_, mutableRhs, statistics);
     }
     else
@@ -102,6 +107,8 @@ public:
 
       // The setMatrix method stores only the selected entries of the matrix (determined by the ignore field)
       solver.setMatrix(*matrix_,&ignore);
+      // get the error code from Cholmod in case something happened
+      errorCode_ = solver.cholmodCommonObject().status;
 
       auto modifiedRhs = *rhs_;
 
@@ -149,6 +156,19 @@ public:
     }
   }
 
+  /** \brief return the error code of the Cholmod factorize call
+   *
+   * In setMatrix() the matrix factorization takes place and Cholmod is
+   * able to communicate error codes of the factorization in the status
+   * field of the cholmodCommonObject.
+   * The return value 0 means "good" and the other values can be found
+   * in the Cholmod User Guide.
+   */
+  int errorCode() const
+  {
+    return errorCode_;
+  }
+
   //! Pointer to the system matrix
   const MatrixType* matrix_;
 
@@ -157,6 +177,9 @@ public:
 
   //! Pointer to the right hand side
   const VectorType* rhs_;
+
+  //! error code of Cholmod factorize call
+  int errorCode_ = 0;
 };
 
 }   // namespace Solvers