about cdiff

[lifei]

  Hi all,   I am confused when using cdiff() function, the help doc tells that "Result values at the grid boundaries are set to missing", and I have difficulties when coping with writing the .ctl file created by that function.   My initial .grd data have a horizontal resolution of 360*180,with one time and height level,that is 360*180*4=259200bytes, when I use cdiff() function, it is 260640bytes, which means 360*181*4 or 362*180*4, by the way, I made the centered difference operation along the x and y direction and created two .grd files by using the "fwrite" command. When I display the new data , it only shows the ground map, and "Contouring: nan to nan interval inf ". Please give me some help by writing "XDEF and YDEF" in the newly created .ctl file .  Thanks!                                                  Eric
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