Thank you very much it worked miracles. But when I checked the result, I found out that sum of weight(i)*target(i) didn't equal to sum of weight(i)*target_new(i), which I need for my problem. How can I add such a constraint in the code? Moreover, I still wonder what is the difference between PROC HPNLMOD and NLMIXED that result the situation I encountered? Is there a specific method HPNLMOD use and another for NLMIXED. Thank you again for your so helpful reply.
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