typo-fix by Kunda

[tools/medcoupling.git] / doc / user / doxygen / doxfiles / examples / medcouplingexamplesmeshes.doxy

\section ExamplesMeshes Meshes

\subsection ExamplesMeshesCreate Create

\subsubsection medcouplingcppexamplesUmeshStdBuild1 Standard build of an unstructured mesh from scratch

Firstly retrieve basic data in full interlace mode for coordinates, and nodal connectivity cell per cell.
\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshStdBuild1_1

Then create MEDCoupling::MEDCouplingUMesh instance giving its mesh dimension (2 here) and a name.

\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshStdBuild1_2

Gives an upper bound of the number of cells to be inserted into the unstructured mesh.
\n Then enter nodal connectivity of all cells, cell per cell using MEDCoupling::MEDCouplingUMesh::insertNextCell method.
\n When the nodal connectivity cell per cell has been finished, call MEDCoupling::MEDCouplingUMesh::finishInsertingCells method in order to restore \b mesh instance.

\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshStdBuild1_3

At this level the connectivity part of the mesh \b mesh as been defined. Now let's set the coordinates using array \b coords defined above.

\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshStdBuild1_4

At this level mesh is usable. When this mesh is no more needed simply call decrRef to decrement its reference counter.

\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshStdBuild1_5


\subsubsection medcouplingcppexamplesUmeshAdvBuild1 Advanced build of an unstructured mesh from scratch

Firstly retrieve basic data in full interlace mode for coordinates, and nodal connectivity cell per cell, cell type \b included (3 for INTERP_KERNEL::NORM_TRI3 and 4 for INTERP_KERNEL::QUAD4).
\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshAdvBuild1_1

Then create MEDCoupling::MEDCouplingUMesh instance giving its mesh dimension (2 here) and a name.

\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshAdvBuild1_2

Then enter nodal connectivity at once.

\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshAdvBuild1_3

At this level the connectivity part of the mesh \b mesh as been defined. Now let's set the coordinates using array \b coords defined above.

\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshAdvBuild1_4

At this level mesh is usable. When this mesh is no more needed simply call decrRef() to decrement its reference counter.

\snippet MEDCouplingExamplesTest.cxx CppSnippetUMeshAdvBuild1_5


\subsubsection medcouplingcppexamplesCmeshStdBuild1 Standard build of an cartesian mesh from scratch

We are going to build a 2D cartesian mesh, constituted from 9 nodes along X axis, and 7 nodes along Y axis.

Firstly retrieve for each direction the discretization and build a \ref MEDCoupling::DataArrayDouble "DataArrayDouble instance" on the corresponding direction.

\snippet MEDCouplingExamplesTest.cxx CppSnippetCMeshStdBuild1_1

Then create MEDCoupling::MEDCouplingCMesh instance giving the 2 instances of \ref MEDCoupling::DataArrayDouble "DataArrayDouble" obtained above.

There are 2 techniques to get it.

Either :

\snippet MEDCouplingExamplesTest.cxx CppSnippetCMeshStdBuild1_2

Or :

\snippet MEDCouplingExamplesTest.cxx CppSnippetCMeshStdBuild1_2bis

\c mesh is now available for use :

\snippet MEDCouplingExamplesTest.cxx CppSnippetCMeshStdBuild1_3

When this mesh is no more needed simply call decrRef to decrement its reference counter (nothing
to be done in Python).

\snippet MEDCouplingExamplesTest.cxx CppSnippetCMeshStdBuild1_4


\subsubsection cpp_mcumesh_buildBoundaryMesh Getting a bounding mesh

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildBoundaryMesh_1
Now we use
\ref MEDCoupling::MEDCouplingUMesh::buildBoundaryMesh "buildBoundaryMesh()" to get a mesh
of lower dimension bounding \b mesh.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildBoundaryMesh_2
Depending on the value of a parameter,
\ref MEDCoupling::MEDCouplingUMesh::buildBoundaryMesh "buildBoundaryMesh()"
creates the mesh sharing the node coordinates array with \b mesh or not.


\subsubsection cpp_mcumesh_buildFacePartOfMySelfNode Retrieving a lower dimension mesh based on given nodes

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildFacePartOfMySelfNode_1
In the following code we retrieve nodes of the cell #0 an then we call
\ref MEDCoupling::MEDCouplingUMesh::buildFacePartOfMySelfNode "buildFacePartOfMySelfNode()"
twice with these nodes and with varying last parameter \b allNodes as input.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildFacePartOfMySelfNode_2
<br>If the last parameter is \c true
\ref MEDCoupling::MEDCouplingUMesh::buildFacePartOfMySelfNode "buildFacePartOfMySelfNode()" looks
for segments whose all nodes are given to it, hence it finds segments bounding the cell #0 only.
<br>If the last parameter is \c false
\ref MEDCoupling::MEDCouplingUMesh::buildFacePartOfMySelfNode "buildFacePartOfMySelfNode()" looks
for any segment whose nodes are given to it, hence it adds more segments to \b mesh2.


\subsubsection cpp_mcumesh_buildPartOfMySelfNode Copying cells selected by nodes

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildPartOfMySelfNode_1
In the following code we retrieve nodes of the cell #0 an then we call
\ref MEDCoupling::MEDCouplingUMesh::buildPartOfMySelfNode "buildPartOfMySelfNode()"
twice with these nodes and with varying last parameter \b allNodes as input.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildPartOfMySelfNode_2
<br>If the last parameter is \c true
\ref MEDCoupling::MEDCouplingUMesh::buildPartOfMySelfNode "buildPartOfMySelfNode()" looks
for cells whose all nodes are given to it, hence it finds the cell #0 only.
<br>If the last parameter is \c false
\ref MEDCoupling::MEDCouplingUMesh::buildPartOfMySelfNode "buildPartOfMySelfNode()" looks
for any cell whose nodes are given to it, hence it finds all cells of \b mesh because all
cells share the node #4.


\subsubsection cpp_mcumesh_buildPartOfMySelf Getting a part of mesh

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildPartOfMySelf_1
Now we use
\ref MEDCoupling::MEDCouplingUMesh::buildPartOfMySelf "buildPartOfMySelf()" to get a mesh
containing only two cells of \b mesh.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildPartOfMySelf_2


\subsection ExamplesMeshesModify Modify

\subsubsection cpp_mcumesh_findAndCorrectBadOriented3DExtrudedCells Fixing orientation of "extruded" volumes

First, we create a mesh with 2 incorrectly oriented "extruded" volumes.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_findAndCorrectBadOriented3DExtrudedCells_1
Now we check that
\ref MEDCoupling::MEDCouplingUMesh::findAndCorrectBadOriented3DExtrudedCells "findAndCorrectBadOriented3DExtrudedCells()"
finds and fixes the reversed cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_findAndCorrectBadOriented3DExtrudedCells_2


\subsubsection cpp_mcumesh_arePolyhedronsNotCorrectlyOriented Fixing orientation of polyhedra

First, we create a mesh with 2 polyhedra, one of which is incorrectly oriented. We create
two "extruded" polyhedra and then convert them to correctly defined polyhedra.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_arePolyhedronsNotCorrectlyOriented_1
Now we check that
\ref MEDCoupling::MEDCouplingUMesh::arePolyhedronsNotCorrectlyOriented "arePolyhedronsNotCorrectlyOriented()"
finds one reversed cell. After that we fix it using
\ref MEDCoupling::MEDCouplingUMesh::orientCorrectlyPolyhedrons "orientCorrectlyPolyhedrons()" and
re-check the orientation of polyhedra.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_arePolyhedronsNotCorrectlyOriented_2


\subsubsection cpp_mcumesh_are2DCellsNotCorrectlyOriented Fixing orientation of faces

First, we create a 2D mesh in 3D space with 3 QUAD4 and 2 TRI3 cells. Orientation of the cell #1 is
reversed comparing with others.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_are2DCellsNotCorrectlyOriented_1
Now we check that
\ref MEDCoupling::MEDCouplingUMesh::are2DCellsNotCorrectlyOriented "are2DCellsNotCorrectlyOriented()"
finds one reversed face. After that we fix the incorrectly oriented cell using
\ref MEDCoupling::MEDCouplingUMesh::orientCorrectly2DCells "orientCorrectly2DCells()" and
re-check the orientation of cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_are2DCellsNotCorrectlyOriented_2


\subsubsection cpp_mcumesh_renumberNodesInConn Renumbering nodes in the connectivity array

First, we create a 2D mesh with 1 QUAD4 cell and with undefined coordinates of nodes.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_renumberNodesInConn_1
Now we use
\ref MEDCoupling::MEDCouplingUMesh::renumberNodesInConn "renumberNodesInConn()"
to get the following nodal connectivity of a sole cell: 0,1,2,3.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_renumberNodesInConn_2
\b old2newIds array defines how node ids are changed:
- new id of node #0 is -1,
- new id of node #1 is 3,
- new id of node #2 is 4,
- new id of node #3 is 1,
- new id of node #4 is 0.


\subsubsection cpp_mcumesh_renumberNodes Renumbering nodes

First, we create a 2D mesh with 4 nodes and no cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_renumberNodes_1
Next, we use
\ref MEDCoupling::MEDCouplingUMesh::renumberNodes "renumberNodes()"
to permute nodes so that
- old node #0 becomes #2,
- old node #1 remains #1,
- old node #2 becomes #0,
- old node #3 is removed.

Number of nodes becomes 3.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_renumberNodes_2

Next we compare behavior of
\ref MEDCoupling::MEDCouplingUMesh::renumberNodes "renumberNodes()" and that of
\ref MEDCoupling::MEDCouplingUMesh::renumberNodes2 "renumberNodes2()" which, in contrast to
\ref MEDCoupling::MEDCouplingUMesh::renumberNodes "renumberNodes()",
moves merged nodes to their barycenter.<br>
We set #2 as new id of old node #3 and expect that
\ref MEDCoupling::MEDCouplingUMesh::renumberNodes2 "renumberNodes2()" moves old nodes #0
and #3 to their barycenter (-0.3,0.0) which becomes position of node #2.<br>
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_renumberNodes_3


\subsubsection cpp_mcumesh_mergeNodes Merging equal nodes

First, we create a 2D mesh with 1 QUAD4 and 2 TRI3 cells. The cells are based on 6 nodes
of which 2 nodes fully coincide (#3 and #4) and 3 nodes are equal with precision 0.003.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_mergeNodes_1
Now we merge node duplicates using
\ref MEDCoupling::MEDCouplingUMesh::mergeNodes "mergeNodes()" and check values it returns.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_mergeNodes_2
Contents of \b arr shows ids of old nodes after the merging. The nodes considered equal
one to the other have the same id in \b arr.

Next we compare behavior of
\ref MEDCoupling::MEDCouplingUMesh::mergeNodes "mergeNodes()" and that of
\ref MEDCoupling::MEDCouplingUMesh::mergeNodes2 "mergeNodes2()" which, in contrast to
\ref MEDCoupling::MEDCouplingUMesh::mergeNodes "mergeNodes()",
moves merged nodes to their barycenter.<br> We expect that
\ref MEDCoupling::MEDCouplingUMesh::mergeNodes2 "mergeNodes2()" moves old nodes #0, #2
and #5 to their barycenter equal to position of node #2.<br>
First we check that
\ref MEDCoupling::MEDCouplingUMesh::mergeNodes "mergeNodes()" does not move nodes
coincident with the node #2 to the position of node #2, and then we check that
\ref MEDCoupling::MEDCouplingUMesh::mergeNodes "mergeNodes2()" does move.
(We check only the second (Y) component of node coordinates since the first component of
these nodes is exactly same.)
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_mergeNodes_3


\subsubsection cpp_mcumesh_zipConnectivityTraducer Removing cell duplicates

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells, so that
- the cell #2 has the same nodal connectivity as the cell #1 does,
- the cell #3 has the same nodal connectivity as the cell #0 does,
- the cell #4 is based on the same nodes as the cell #0 but nodes order is different.

\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_zipConnectivityTraducer_1
Now we use
\ref MEDCoupling::MEDCouplingUMesh::zipConnectivityTraducer "zipConnectivityTraducer()"
to remove duplicate cells. Then we check that two cells, having exactly same nodal
connectivity with other cells, have been removed.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_zipConnectivityTraducer_2
Contents of \b arr shows ids of cells after duplicates removal. If a value (cell id)
equals to its index in \b arr, this means that the cell is not a duplicate of any cell
with lower id. Else, the value gives a cell id to which this cell is equal. <br>
Thus, the cells #0 and #1 have no preceding equal cell since \b arr[i] == i.<br>
The cell #2 equals to the cell #1 (== \b arr[2] ).<br>
The cell #3 equals to the cell #0 (== \b arr[3] ).<br>
The cell #4 has no equal cell. This is because the cell comparison technique specified
when we called
\ref MEDCoupling::MEDCouplingUMesh::zipConnectivityTraducer "zipConnectivityTraducer()"
was 0 ("exact"), if we had used the technique 2 ("nodal"), \b arr[4] would be 0.


\subsubsection cpp_mcumesh_zipCoordsTraducer Removing unused nodes

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_zipCoordsTraducer_1
Now we create \b mesh2 including all nodes but only two cells of \b mesh, and we use \ref
MEDCoupling::MEDCouplingUMesh::zipCoordsTraducer "zipCoordsTraducer()" to remove unused
nodes from \b mesh2.
\ref MEDCoupling::MEDCouplingUMesh::zipCoordsTraducer "zipCoordsTraducer()" returns an array
with -1 for unused nodes and new ids for used ones.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_zipCoordsTraducer_2


\subsubsection cpp_mcumesh_getNodeIdsInUse Retrieving unused nodes

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getNodeIdsInUse_1
Now we create \b mesh2 including all nodes but only two cells of \b mesh, and we use \ref
MEDCoupling::MEDCouplingUMesh::getNodeIdsInUse "getNodeIdsInUse()" to get nodes of \b mesh2
used in its two cells.
\ref MEDCoupling::MEDCouplingUMesh::getNodeIdsInUse "getNodeIdsInUse()" returns an array
with -1 for unused nodes and new ids for used ones.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getNodeIdsInUse_2
Now we use \b newNbOfNodes returned by
\ref MEDCoupling::MEDCouplingUMesh::getNodeIdsInUse "getNodeIdsInUse()" to convert \b arr
to "New to Old" mode.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getNodeIdsInUse_3


\subsubsection cpp_mcumesh_convertToPolyTypes Conversion of cells to "poly" types

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_convertToPolyTypes_1
Now we convert cells #1 and #3 to type POLYGON and check the result
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_convertToPolyTypes_2


\subsubsection cpp_mcpointset_scale Scaling the mesh

First, we create a 2D mesh with 4 nodes and no cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_scale_1
Then we scale it by a factor of 2 with a center (0.,0.).
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_scale_2
Finally we check that all node coordinates have changed by more than 0.9.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_scale_3


\subsubsection cpp_mcpointset_translate Translating the mesh

First, we create a 2D mesh with 4 nodes and no cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_translate_1
Then we translate it by a vector (1.,1.).
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_translate_2
Finally we check that all node coordinates have changed by more than 0.9.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_translate_3


\subsubsection cpp_mcpointset_rotate Rotating the mesh

First, we create a 2D mesh with 4 nodes and no cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_rotate_1
Then we rotate it around a point (0.,0.) by 90 degrees clockwise.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_rotate_2
Next, we make a 3D mesh from the 2D one and rotate it around the Z axis by 90 degrees
counter-clockwise.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_rotate_3
Finally we transform the mesh back to 2D space and check that all nodes get back to the
initial location.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_rotate_4


\subsection ExamplesMeshesAccess Access

\subsubsection cpp_mccmesh_getCoordsAt Getting node coordinates along an axis

We create an 1D Cartesian mesh and retrieves node coordinates using
\ref MEDCoupling::MEDCouplingCMesh::getCoordsAt "getCoordsAt()".
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingCMesh_getCoordsAt_1


\subsubsection cpp_mcpointset_getcoordinatesofnode Getting coordinates of a node

The following code creates a 2D \ref MEDCoupling::MEDCouplingUMesh
"MEDCouplingUMesh" with 3 nodes and no cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_getCoordinatesOfNode_1
Here we get coordinates of the second node and check its two coordinates.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_getCoordinatesOfNode_2


\subsubsection cpp_mcumesh_areCellsIncludedIn Cells correspondence in two meshes

First, we create a 2D \b mesh1 with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_areCellsIncludedIn_1
Then we create a \b mesh2 which includes cells #4, #2 and #0 of \b mesh1. The two meshes
share the same node coordinates array.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_areCellsIncludedIn_2
Now we ascertain that
- \ref MEDCoupling::MEDCouplingUMesh::areCellsIncludedIn "areCellsIncludedIn()"
detects that all cells of \b mesh2 are present in \b mesh1,
-  the correspondence array \b corr2to1, which gives cell ids of \b mesh2 within
\b mesh1, is equal to the array \b cells2 which selected cells from \b mesh1 for creation
of \b mesh2.

\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_areCellsIncludedIn_3
Now we apply
\ref MEDCoupling::MEDCouplingUMesh::areCellsIncludedIn "areCellsIncludedIn()"
in a reverse direction and ascertain that it returns \c false.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_areCellsIncludedIn_4
The contents of the correspondence
array \b corr1to2 [2, 3, 1, 4, 0] means the following.
- The cell #0 of \b mesh1 is equal to the cell #2 (== \b corr1to2[ 0 ]) of \b mesh2.
- The cell #1 of \b mesh1 is missing from \b mesh2 (as \b corr1to2[ 1 ] >= \b mesh2->getNumberOfCells()).
- The cell #2 of \b mesh1 is equal to the cell #1 (== \b corr1to2[ 2 ]) of \b mesh2.
- The cell #3 of \b mesh1 is missing from \b mesh2 (as \b corr1to2[ 3 ] >= \b mesh2->getNumberOfCells()).
- The cell #4 of \b mesh1 is equal to the cell #0 (== \b corr1to2[ 4 ]) of \b mesh2.


\subsubsection cpp_mcumesh_checkDeepEquivalWith Deep comparison of meshes

First, we create two 2D meshes with two triangles, so that
- their nodes are almost same but permuted,
- the first triangle is based exactly on the same nodes (taking the permutation into account),
- an order of nodes in the second triangle is changed.

\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_checkDeepEquivalWith_1
Then we check that
- \ref MEDCoupling::MEDCouplingUMesh::checkDeepEquivalWith "checkDeepEquivalWith()"
considers the meshes equal (i.e. it does not throw any exception) if it is called with a cell
comparison policy \b cellCompPol == 1
-  mapping from \b mesh1 to \b mesh2 for both nodes and cells is as expected.

\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_checkDeepEquivalWith_2
Next we ascertain that
\ref MEDCoupling::MEDCouplingUMesh::checkDeepEquivalOnSameNodesWith "checkDeepEquivalOnSameNodesWith()"
consider \b mesh1 and \b mesh2 different as they do not share the same nodal connectivity
array. <br>
After that we make the meshes share the node coordinates array and insert new
triangles based on the same nodes but in different order. This is to ascertain that
\ref MEDCoupling::MEDCouplingUMesh::checkDeepEquivalOnSameNodesWith "checkDeepEquivalOnSameNodesWith()"
called with the weakest cell comparison policy considers the meshes equal.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_checkDeepEquivalWith_3


\subsubsection cpp_mcumesh_getPartBarycenterAndOwner Getting barycenters of cells

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getPartMeasureField_1
Now we use
\ref MEDCoupling::MEDCouplingUMesh::getPartBarycenterAndOwner "getPartBarycenterAndOwner()" to get
barycenters of all but the first cell.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getPartMeasureField_3
The returned array contains 4 tuples per 2 components.


\subsubsection cpp_mcumesh_getCellsContainingPoints Finding cells containing a point (multi-point case)

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellsContainingPoints_1
Then we use
\ref MEDCoupling::MEDCouplingUMesh::getCellsContainingPoints "getCellsContainingPoints()" to
get cells in contact with tree points. Two of them are in contact with some cells and one is not.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellsContainingPoints_2
The contents of the result arrays \b cells ([4, 0, 1]) and \b cellsIndex ([0, 0, 1, 3])
mean the following.
- Point #0 is in contact with none (== \b cellsIndx[1] - \b cellsIndx[0]) cell.
- Point #1 is in contact with 1 (== \b cellsIndx[2] - \b cellsIndx[1]) cell whose id is #4
  (== \b cells[ \b cellsIndx[ 1 ]]).
- Point #2 is in contact with 2 (== \b cellsIndx[3] - \b cellsIndx[2]) cells whose ids are #0
  (== \b cells[ \b cellsIndx[ 2 ]]) and #1 (== \b cells[ \b cellsIndx[ 2 ] + 1 ]).


\subsubsection cpp_mcumesh_getCellsContainingPoint Finding cells containing a point

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellsContainingPoint_1
Then we use
\ref MEDCoupling::MEDCouplingUMesh::getCellsContainingPoint "getCellsContainingPoint()" to
get cells in contact with a small ball (point with precision) located near the node #4 and
shifted from this node by its radius \b eps.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellsContainingPoint_2
Since the node #4 is shared by all cells, size of the vector \b cellIds must be equal to
the number of cells in \b mesh.


\subsubsection cpp_mcumesh_buildPartOrthogonalField Getting normals of cells

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells. Orientation of the cell #1 is
reversed.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildPartOrthogonalField_1
Now we use
\ref MEDCoupling::MEDCouplingUMesh::buildPartOrthogonalField "buildPartOrthogonalField()" to get
normal vectors to the cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildPartOrthogonalField_2


\subsubsection cpp_mcumesh_getPartMeasureField Getting volumes of cells

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells. Orientation of the cell #1 is
reversed.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getPartMeasureField_1
Now we use
\ref MEDCoupling::MEDCouplingUMesh::getPartMeasureField "getPartMeasureField()" to get
volumes of all but the first cell. If we call
\ref MEDCoupling::MEDCouplingUMesh::getPartMeasureField "getPartMeasureField()" with \b
isAbs == \c true, the area of the cell #1 is returned positive, else, negative that
reflects its inverse orientation.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getPartMeasureField_2


\subsubsection cpp_mcumesh_getCellsInBoundingBox Getting cells using the bounding box

First, we create a 2D mesh with 1 TRI3 cell. Bounding box of this cell is [0.,0., 1.,1].
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellsInBoundingBox_1
Now we check how
\ref MEDCoupling::MEDCouplingUMesh::getCellsInBoundingBox "getCellsInBoundingBox()"
searches for cells using the bounding box. We use a bounding box touching the bounding box
of the sole cell at one point (1.,1.).
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellsInBoundingBox_2
If \ref MEDCoupling::MEDCouplingUMesh::getCellsInBoundingBox "getCellsInBoundingBox()" is
called with parameter \b eps == 0.0, the cell is not found because the two bounding boxes
(one of the cell and the one passed as parameter) do not overlap. <br>
If \ref MEDCoupling::MEDCouplingUMesh::getCellsInBoundingBox "getCellsInBoundingBox()" is
called with parameter \b eps == 0.1, the cell is found because \b eps is used to increase
the bounding box of the cell and thus the two bounding boxes intersect each other. <br>


\subsubsection cpp_mcumesh_findBoundaryNodes Getting boundary nodes

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_findBoundaryNodes_1
Now we use
\ref MEDCoupling::MEDCouplingUMesh::findBoundaryNodes "findBoundaryNodes()" to get ids
of boundary nodes.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_findBoundaryNodes_2
\ref MEDCoupling::MEDCouplingUMesh::findBoundaryNodes "findBoundaryNodes()" returns all
node ids except the node #4 which is in the middle of \b mesh.


\subsubsection cpp_mcumesh_getCellIdsLyingOnNodes Getting cells by nodes

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellIdsLyingOnNodes_1
In the following code we retrieve nodes of the cell #0 an then we call
\ref MEDCoupling::MEDCouplingUMesh::getCellIdsLyingOnNodes "getCellIdsLyingOnNodes()"
twice with these nodes and with varying last parameter \b allNodes as input.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellIdsLyingOnNodes_2
<br>If the last parameter is \c true
\ref MEDCoupling::MEDCouplingUMesh::getCellIdsLyingOnNodes "getCellIdsLyingOnNodes()" looks
for cells whose all nodes are given to it, hence it finds the cell #0 only.
<br>If the last parameter is \c false
\ref MEDCoupling::MEDCouplingUMesh::getCellIdsLyingOnNodes "getCellIdsLyingOnNodes()" looks
for any cell whose nodes are given to it, hence it finds all cells of \b mesh because all
cells share the node #4.


\subsubsection cpp_mcumesh_getCellIdsFullyIncludedInNodeIds Getting cells by nodes

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellIdsFullyIncludedInNodeIds_1
In the following code we retrieve nodes of two cells an then we use
\ref MEDCoupling::MEDCouplingUMesh::getCellIdsFullyIncludedInNodeIds
"getCellIdsFullyIncludedInNodeIds()" to find these cells by their nodes.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getCellIdsFullyIncludedInNodeIds_2


\subsubsection cpp_mcumesh_buildDescendingConnectivity2 Retrieving the descending connectivity with orientation

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildDescendingConnectivity2_1
Now we get and check the descending connectivity.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildDescendingConnectivity2_2
Here we get connectivity of the cell #2 (#3 in FORTRAN mode) of \b mesh2 to see how
mutual orientation of cells in \b mesh and \b mesh2 is defined.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildDescendingConnectivity2_3
The contents of the result arrays \b desc and \b descIndx mean the following.
- The cell #0 of \b mesh (QUAD4) is bound by 4 (== \b descIndx[1] - \b descIndx[0])
  segments (SEG2) of \b mesh2 whose ids in FORTRAN mode are
  - #1 (== \b desc[ \b descIndx[ 0 ]]),
  - #2 (== \b desc[ \b descIndx[ 0 ] + 1 ]),
  - #3 (== \b desc[ \b descIndx[ 0 ] + 2 ]) and
  - #4 (== \b desc[ \b descIndx[ 0 ] + 3 ]).
  <br>Ids are positive since order of nodes in the corresponding cells of \b mesh and \b mesh2
  are same. For example nodes of SEG2 #3 are [4,1] and nodes of QUAD4 #0 are [0,3,\b 4,\b 1].
- The cell #1 of \b mesh (TRI3) is bound by 3 (== \b descIndx[2] - \b descIndx[1]) segments of
  \b mesh2 whose ids in FORTRAN mode are:
  - #-3 (== \b desc[ \b descIndx[ 1 ]]),
  - #5 (== \b desc[ \b descIndx[ 1 ] + 1 ]) and
  - #6 (== \b desc[ \b descIndx[ 1 ] + 2 ]).
  <br>The id -3 means that order of nodes in SEG2 #3 ([4,1]) is different from the order of
  these nodes in TRI3 #1: [\b 1,\b 4,2].
- etc.

The contents of the result arrays \b revDesc and \b revDescIndx mean the following.
- The cell #0 of \b mesh2 (SEG2) bounds 1 (== \b revDescIndx[1] - \b revDescIndx[0]) cell of \b
  mesh whose id is:
  - # 0 (== \b revDesc[ \b revDescIndx[ 0 ]]).
- The cell #1 of \b mesh2 bounds 2 (== \b revDescIndx[2] - \b revDescIndx[1]) cells of \b
  mesh whose ids are:
  - # 0 (== \b revDesc[ \b revDescIndx[ 1 ]]) and
  - # 1 (== \b revDesc[ \b revDescIndx[ 1 ] + 1 ]).
- etc.


\subsubsection cpp_mcumesh_buildDescendingConnectivity Retrieving the descending connectivity

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildDescendingConnectivity_1
Now we get and check the descending connectivity.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_buildDescendingConnectivity_2
The contents of the result arrays \b desc and \b descIndx mean the following.
- The cell #0 of \b mesh (QUAD4) is bound by 4 (== \b descIndx[1] - \b descIndx[0])
  segments (SEG2) of \b mesh2 whose ids are
  - #0 (== \b desc[ \b descIndx[ 0 ]]),
  - #1 (== \b desc[ \b descIndx[ 0 ] + 1 ]),
  - #2 (== \b desc[ \b descIndx[ 0 ] + 2 ]) and
  - #3 (== \b desc[ \b descIndx[ 0 ] + 3 ]).
- The cell #1 of \b mesh (TRI3) is bound by 3 (== \b descIndx[2] - \b descIndx[1]) segments of
  \b mesh2 whose ids are:
  - #2 (== \b desc[ \b descIndx[ 1 ]]),
  - #4 (== \b desc[ \b descIndx[ 1 ] + 1 ]) and
  - #5 (== \b desc[ \b descIndx[ 1 ] + 2 ]).
- etc.

The contents of the result arrays \b revDesc and \b revDescIndx mean the following.
- The cell #0 of \b mesh2 (SEG2) bounds 1 (== \b revDescIndx[1] - \b revDescIndx[0]) cell of \b
  mesh whose id is:
  - # 0 (== \b revDesc[ \b revDescIndx[ 0 ]]).
- The cell #1 of \b mesh2 bounds 2 (== \b revDescIndx[2] - \b revDescIndx[1]) cells of \b
  mesh whose ids are:
  - # 0 (== \b revDesc[ \b revDescIndx[ 1 ]]) and
  - # 1 (== \b revDesc[ \b revDescIndx[ 1 ] + 1 ]).
- etc.


\subsubsection cpp_mcumesh_getReverseNodalConnectivity Getting the reverse nodal connectivity

First, we create a 2D mesh with 3 QUAD4 and 2 TRI3 cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getReverseNodalConnectivity_1
Now we get and check its reverse nodal connectivity.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingUMesh_getReverseNodalConnectivity_2
The contents of the result arrays mean the following.
- Node #0 is shared by 1 (== \b revNodalIndx[1] - \b revNodalIndx[0]) cell whose id is #0
  (== \b revNodal[ \b revNodalIndx[ 0 ]]).
- Node #1 is shared by 2 (== \b revNodalIndx[2] - \b revNodalIndx[1]) cells whose ids are #0
  (== \b revNodal[ \b revNodalIndx[ 1 ]]) and #1 (== \b revNodal[ \b revNodalIndx[ 1 ] + 1 ]).
- etc.


\subsubsection cpp_mcpointset_getBoundingBox Getting a minimum box bounding nodes

First, we create a 3D mesh with 2 nodes, so that the first one has minimal coordinates and
the second one has maximal coordinates.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_getBoundingBox_1
Now we get a bounding box enclosing these nodes. This bounding box should contain
coordinates of our two nodes (but in "no interlace" mode), as the nodes coincide with
points returned by the bounding box.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_getBoundingBox_2


\subsubsection cpp_mcpointset_getnodeidsnearpoint Getting nodes close to a point

The following code creates a 2D \ref MEDCoupling::MEDCouplingUMesh
"MEDCouplingUMesh" with 5 nodes and no cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_getNodeIdsNearPoint_1
Now we define an array of coordinates of a point close to nodes #0, #2 and #4.

Thus we expect that
\ref MEDCoupling::MEDCouplingPointSet::getNodeIdsNearPoint "getNodeIdsNearPoint()" that
we are going to use,
if called with \b eps = 0.003, would return ids of nodes #0, #2 and #4.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_getNodeIdsNearPoint_2


\subsubsection cpp_mcpointset_getnodeidsnearpoints Getting nodes close to some points

The following code creates a 2D \ref MEDCoupling::MEDCouplingUMesh
"MEDCouplingUMesh" with 7 nodes and no cells.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_getNodeIdsNearPoints_1
Now we define an array of coordinates of 3 points near which we want to find nodes of the mesh.
- Point #0 is at distance 0.001 from the node #1.
- Point #1 is rather far from all nodes.
- Point #2 is close to nodes #3, #4 and #5.

Thus we expect that
\ref MEDCoupling::MEDCouplingPointSet::getNodeIdsNearPoints "getNodeIdsNearPoints()" that
we are going to use,
if called with \b eps = 0.003, would return ids of close nodes #1, #3, #4 and #5.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_getNodeIdsNearPoints_2
\b idsIndex returns [0, 1, 1, 4] which means that:
- Point #0 is close to 1 (== \b idsIndex[1] - \b idsIndex[0]) node whose id is
\b ids[ \b idsIndex[ 0 ]].
- Point #1 is close to 0 (== \b idsIndex[2] - \b idsIndex[1]) nodes.
- Point #2 is close to 3 (== \b idsIndex[3] - \b idsIndex[2]) nodes whose ids are
\b ids[ \b idsIndex[ 2 ]], \b ids[ \b idsIndex[ 2 ] + 1 ] and \b ids[ \b idsIndex[ 2 ] + 2 ].


\subsubsection cpp_mcpointset_findcommonnodes Finding coincident nodes

First, we create a mesh with 6 nodes, of which two nodes (#3 and #4) are fully coincident
and 3 nodes (#0, #2 and #5) have distance less than 0.004 between them.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_findCommonNodes_1
Then, we use \ref MEDCoupling::MEDCouplingPointSet::findCommonNodes() "findCommonNodes()" to find
coincident nodes, and check that (1) calling
\ref MEDCoupling::MEDCouplingPointSet::findCommonNodes() "findCommonNodes()" with \b prec
== 1e-13 finds the two fully coincident nodes only and (2)
\ref MEDCoupling::MEDCouplingPointSet::findCommonNodes() "findCommonNodes"(0.004) finds 5
equal nodes.
\snippet MEDCouplingExamplesTest.cxx CppSnippet_MEDCouplingPointSet_findCommonNodes_2