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RE: [ccp4bb]: I to F's
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> Using the quadratic relation obtained from
> I + SIGI = (F+SIGF) (F+SIGF)
> 2F SIGF + SIGF*SIGF = SIGI
> So you can solve for SIGF.
> When SIGF <<< F, SIGF ~~ SIGI/2F but this is not true for small F.
[Alexei Botchkarev] This is a particular case. One can modify the
by multiplying and dividing it on sqrt(I + SigI) + sqrt(I)
SigF = sqrt( I + SigI ) - sqrt ( I ) = SigI / [ sqrt(I + SigI) +
sqrt( I ) ] 
When SigI << I, SigF ~~SigI/2 sqrt(I)
When SigI >> I, SigF~~SigI/sqrt(SigI) = sqrt(SigI)
When SigI ~~I,  provides a smooth connection of two extremes.
Alexey Bochkarev, Assistant Professor
Dept. of Biochemistry and Molecular Biology
Univ. of Oklahoma Health Sciences Center, BRC-466
P.O. Box 26901, Oklahoma City, Oklahoma 73190
Phone: (405) 271-8346
FAX : (405) 271-3910