Hi Hao Bo, I suspect your problem is caused by "nRows = 1". Your grid is probably really the product of numbers of rows and columns both significantly larger than 1. You need to use these values, rather than setting nRows = 1 and nCols = the number of points in your grid. Rather, you need to factor the number of grid points into nRows * nCols where both are > 1. Good luck, Bill
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