LINEINTRGAL Line Integral in a 2D Vector Field.
LINEINTRGAL(X,Y,U,V,C) computes the line integral along the lines given in cell array C.
X and Y define the coordinates of a rectangular grid over which
U and V are defined. X and Y must be monotonic and 2D plaid as
％ produced by MESHGRID. X, Y, U, and V must all be the same size.
