NAME:definetri PURPOSE:Define a triangulation array like TRIANGULATE. But in a VERY SIMPLE CASE: the points are regulary-gridded on nx*ny array. Find a Delaunay triangulation for this set of points is easy: Points define (nx-1)*(ny-1) rectangles which we can cut in 2 triangles. cf. figure above ny-1*---*---*. . . . . .*---*---* | /| /| | /| /| | / | / | | / | / | |/ |/ | |/ |/ | ny-2*---*---*. . . . . .*---*---* . . . . . . . . . . . . 1*---*---*. . . . . .*---*---* | /| /| | /| /| | / | / | | / | / | |/ |/ | |/ |/ | 0*---*---*. . . . . .*---*---* 0 1 2 nx-3 nx-2 nx-1 You have 2 ways to cut a rectangle: 1) the upward diagonal 2) the downward diagonal *---* *---* | /| |\ | | / | | \ | |/ | | \| *---* *---* CATEGORY: to understand how TRIANGULATE and TRIANGULATION work! CALLING SEQUENCE:triangles=definetri(nx, ny [,downward]) INPUTS: nx and ny are the array dimensions OPTIONAL INPUTS: downward: When downward is undefine all rectangles are cut in using the upward diagonal. Downward is a vector which contains the rectangles numbers which are cut in using the downward diagonal. The rectangle number is define by the index (in a nx*ny vector) of the lower-left corner of the rectangle. KEYWORD PARAMETERS: OUTPUTS: triangles is a 2d array and is dimensions are 3 and 2*(nx-1)*(ny-1) triangles is define like in the TRIANGULATE procedure. OPTIONAL OUTPUTS: COMMON BLOCKS: SIDE EFFECTS: RESTRICTIONS: PROCEDURE: EXAMPLE: triangles=definetri(3,3,[1,3]) triangles will be a this kind of triangulation: *---*---* |\ | /| | \ | / | | \|/ | *---*---* | /|\ | | / | \ | |/ | \| *---*---*