Returns cell values of the Ith function attached to 3D mesh M3 for cells in the specified CHUNK. The CHUNK may be a list of cell indices, in which case getc3 returns a (CHUNK.shape) array of vertex coordinates. CHUNK may also be a mesh-specific data structure used in the slice3 routine (see "slice3: Plane and Isosurface Slices of a 3-D mesh" on page 65), in which case getc3 may return a (ni)x(nj)x(nk) array of vertex values. There is no savings in the amount of data for such a CHUNK, but the gather operation is cheaper than a general list of cell indices. Use getc3 when writing coloring functions for slice3.
If CHUNK is a CLIST, the additional arguments L, U, FSL, and FSU are vertex index lists which override the CLIST if the Ith attached function is defined on mesh vertices. L and U are index arrays into the (CLIST.shape)x2x2x2 vertex value array, say vva, and FSL and FSU are corresponding interpolation coefficients; the zone centered value is computed as a weighted average of involving these coefficients. The CELLS argument is required by histogram to do the averaging. See the source code for details. By default, this conversion (if necessary) is done by averaging the eight vertex-centered values.
getc3_rect does the job for a regular rectangular mesh.
getc3_irreg: Same thing as getc3_rect, i. e., returns the same type of data structure, but from an irregular mesh. m3  is a 2-list; m3  is an array whose ith element is an array of coordinate indices for the ith cell, or a list of up to four such arrays. m3   is the 3 by nverts array of coordinates. m3  is a list of arrays of vertex-centered or cell-centered data. chunk may be a list, in which case chunk  is a 2-sequence representing a range of cell indices; or it may be a one-dimensional array, in which case it is a nonconsecutive set of cell indices. It is guaranteed that all cells indexed by the chunk are the same type.