OFFSET
0,1
COMMENTS
Define the Fibonacci Function F(x) and its derivative as in A171909.
The derivative is dF/dx = (phi^x * log(phi) - cos(Pi*x)*log(phi)/phi^x + Pi*sin(Pi*x)/phi^x)/sqrt(5).
Set dF(x)/dx = 0 to find the local minimum.
LINKS
Gerd Lamprecht, Iterationsrechner
Gerd Lamprecht, Zahlenfolgen (sequences)
E. Weisstein, Fibonacci Number, Mathworld.
EXAMPLE
F(1.67668837258...) = 0.896946387424606172912600371068765...
MAPLE
p := (1+sqrt(5))/2 ; F := (p^x - cos(Pi*x)/p^x )/sqrt(5);
Fpr := diff(F, x) ; Fpr2 := diff(Fpr, x) ;
Digits := 80 ; x0 := 1.67 ;
for n from 1 to 10 do
x0 := evalf(x0-subs(x=x0, Fpr)/subs(x=x0, Fpr2)) ;
print( evalf(subs(x=x0, F))) ;
end do : # R. J. Mathar, Feb 02 2010
MATHEMATICA
digits = 104; F[x_] := (GoldenRatio^x - Cos[Pi*x]/GoldenRatio^x)/Sqrt[5]; x0 = x /. FindRoot[F'[x], {x, 2}, WorkingPrecision -> digits+1]; RealDigits[F[x0], 10, digits][[1]] (* Jean-François Alcover, Jan 28 2014 *)
PROG
(Other) Gerd Lamprecht online Iterationsrechner: #@P@Q5)*0.5+0.5, x)/@Q5)+@P@Q5)*0.5-0.5, x)*sin(PI*(x-0.5))/@Q5)@Na=0.19; b=1.6; @B2]=2; @N@B0]=Fx(b); @B1]=Fx(b-a); @B2]=Fx(b+a); if(@B0]%3C@B1]&&@B0]%3C@B2])a/=10; @Eif(@B1]%3C@B2])b-=a; @Eb+=a; @N@A@B1]-@B2])%3C1e-17@N1@N1@Nc=Fx(b);
CROSSREFS
KEYWORD
cons,nonn
AUTHOR
Gerd Lamprecht (gerdlamprecht(AT)googlemail.com), Jan 25 2010
EXTENSIONS
Edited, offset and leading zero normalized by R. J. Mathar, Feb 02 2010
STATUS
approved