rcond in polyfit

Charles R Harris charlesr.harris at gmail.com
Thu Oct 12 20:28:31 CDT 2006

Hi all,

I note that polyfit looks like it should work for single and double, real
and complex, polynomials. On the otherhand, the default rcond needs to
depend on the underlying precision. On the other, other hand, all the svd
computations are done with dgelsd or zgelsd, i.e., double precision. Even so
problems can arise from inherent errors of the input data if it is single
precision to start with. I also think the final degree of the fit should be
available somewhere if wanted, as it is an indication of what is going on.
Sooo, any suggestions as to what to do? My initial impulse would be to set
rcond=1e-6 for single, 1e-14 for double, make rcond a keyword, and kick the
can down the road on returning the actual degree of the fit.


PS, what is the best way of converting arbitrary arrays to the appropriate c
data types float and double?
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