Thanks very much Patrick, Henry and Raul for your suggestions.
I did not read far enough down in the dictionary to see I. when looking to solve this problem. I've learned a lot from this simple problem. On my machine: ts 'YISO =: XI interp3 X;Y' 0.360464 1.37946e6 ts 'YIJPH =: (X;Y) lintrp XI' 0.007234 887680 ts 'YIHR =: XI resamp X,:Y' 0.017489 1.54445e6 There is a very small difference (of the order 1e_8, increasing with index and evenly distributed about zero) between Patrick's very fast and memory-efficient version's YI values and those of the other three routines for my example problem. It may be a rounding error, but I have not investigated the reason for the discrepancy yet. plot XI;YISO-YIJPH shows the difference. Sean ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
