CART2IND

CART2IND Find the index value of cartesian coordinates within a grid.
IND = CART2IND[x,y,X,Y] finds the nearest column-wise index value of
cartesian coordinates x and y within the grids defined by X and Y.

-If x and y are vectors of the same length, one index value will be returned
per x y pair.

-X and Y can either be vectors specifying the column and
row coordinates of the grid or coordinate arrays such as produced by
MESHGRID.

-X and Y should be in xy orientation, with X in ascending and
Y in descending order along the vector.

-x,y coordinates that are off the X,Y grid will be returned as NaN.