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documentation/lagrit_manual/commands/negative_aij.txt

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+.. _negative_aij :
+
+&nbsp_place_holder;
+
+> **_NEGATIVE_AIJ_**
+
+>
+
+>> This command tests all edges of all boundary faces for negative coupling
+coefficients.
+
+It adds three attributes to the mesh object:  num_neg_coup_coeff, type=INT,
+length=scalar -number of negative coupling coefficients
+
+neg_coup_coeff, type=VDOUBLE, length=num_neg_coup_coeff - value of coupling
+coefficient
+
+ietet_aij, type=VINT, length=num_neg_coup_coeff,rank=vector -
+
+for each negative coupling coefficient, i: ietet_aij(1,i) contains the
+tetrahedron number which contributes the most negative portion to the coupling
+coefficient, ietet_aij(2,i) contains the local face number that contains the
+local edge (ietet_aij(3,i)) which has the negative coupling coefficient These
+attributes can be used to generate a set of points to be added to the mesh in
+an attempt to reduce the number of negative coupling coefficients by the
+**refine** option. The points added are created by projecting the fourth node
+of the tetrahedron onto the identified face and then projecting this
+projection onto the identified edge. If the final projected point lies between
+the end points of the identified edge, this edge is refined. The
+identification and refinement steps may be iterated up to maxiter times.
+Alternatively the attribute may be used to create an **eltset **of the
+identified elements.
+
+The **rivara** option uses a rivara refinement method to add nodes on exterior
+boundary edges until all coupling coefficients are positive or until a maximum
+number of iterations has been exceeded. FORMAT: **negative_aij**
+
+**negative_aij**/**refine**   
+**negative_aij**/**refine**/maxiter   
+**negative_aij/eltset/**eltset_name   
+**negative_aij/rivara** EXAMPLES: **negative_aij**   
+**negative_aij/refine **only one iteration will be performed   
+**negative_aij/refine/5** a maximum of 5 iterations will be performed   
+**negative_aij**/**eltset**/bad_tets an element set called bad_tets will be made no refinement will be performed/ **negative_aij/rivara**   
+****&nbsp_place_holder; [Click here for demos](../demos/refine_rivara/test/html/main_rivara.html)
+