[R] nlm doesn't detect a gradient in my function - odd solution (bug?)

From: Andrew Robinson <andrewr_at_uidaho.edu>
Date: Wed 21 Jul 2004 - 13:28:30 EST


Dear R community,

I sent a question to the list a few days ago. Using nlm, I was unable to detect a gradient in a four-parameter function that I had written in the region that I was searching, even though the function surface clearly varied in the fourth significant figure there.

I stumbled across a peculiar solution: the nlm function was able to detect a non-zero gradient when the ndigit value was *reduced*. The default value is 12, I was able to detect a gradient in one of the four dimensions if I used 10, and in all of the four if I used 8.

Does that make any sense to anyone?

Thanks,

Andrew



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