XY = MMSTREAM2(X,Y,U,V,X0,Y0,Mark,Step) computes streamlines from gradient data in matrices U and V.
X and Y can be vectors defining the coordinate axes data where U(i,j) and V(i,j) coincide with the coordinates axes points X(j) and Y(i).
Alternatively, X and Y can be 2D plaid matrices as produced by MESHGRID.
X0 and Y0 are equal length vectors defining coordinates that mark the Start, End, or a point On individual streamlines as denoted by the input Mark which is 'Start', 'End' or 'On'. If empty or not given Mark='Start'.
Step identifies the normalized step size used. If empty or not given, Step = 0.1, i.e., 1/10 of a cell. 0.01 <= Step <= 0.5

XY is a cell array containing streamline data points. XY{k}(:,1) contains the x-axis data and XY{k}(:,2) contains the y-axis data for the k-th streamline.