# discretize.TreeMesh.average_node_to_cell#

TreeMesh.average_node_to_cell#

Averaging operator from nodes to cell centers (scalar quantities).

This property constructs a 2nd order averaging operator that maps scalar quantities from nodes to cell centers. This averaging operator is used when a discrete scalar quantity defined on mesh nodes must be projected to cell centers. Once constructed, the operator is stored permanently as a property of the mesh. See notes.

Returns
(n_cells, n_nodes) scipy.sparse.csr_matrix

The scalar averaging operator from nodes to cell centers

Notes

Let $$\boldsymbol{\phi_n}$$ be a discrete scalar quantity that lives on mesh nodes. average_node_to_cell constructs a discrete linear operator $$\mathbf{A_{nc}}$$ that projects $$\boldsymbol{\phi_f}$$ to cell centers, i.e.:

$\boldsymbol{\phi_c} = \mathbf{A_{nc}} \, \boldsymbol{\phi_n}$

where $$\boldsymbol{\phi_c}$$ approximates the value of the scalar quantity at cell centers. For each cell, we are simply averaging the values defined on its nodes. The operation is implemented as a matrix vector product, i.e.:

phi_c = Anc @ phi_n