       Re: How can I get the previous Fibonacci calculated

• To: mathgroup at smc.vnet.net
• Subject: [mg100304] Re: [mg100266] How can I get the previous Fibonacci calculated
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Sun, 31 May 2009 06:36:51 -0400 (EDT)

```prevFib[x_] := Module[{m, n, x2},
x2 = SetPrecision[x, 100];
If[x > 10^15,
N[x/GoldenRatio],
m = (n /. FindRoot[Fibonacci[n] - x2 == 0, {n, 100},
WorkingPrecision -> 100]) - 1;
If[Abs[m - Round[m]] < 10^-10,
Fibonacci[Round[m]],
N[Fibonacci[m]]]]]

prevFib

8

prevFib[Fibonacci] == Fibonacci

True

prevFib[Fibonacci] == Fibonacci

True

prevFib[Fibonacci] == Fibonacci

True

prevFib[234.34*^10]

1.4483008492365037*^12

Bob Hanlon

---- ratulloch at gmail.com wrote:

=============
Greetings

How can I get a previous Fibonacci calculated number in a specific
range.  I can calculate the previous number of phi see below

phi1 =(1+sqrt(5))/2

13/phi1

I tested it with 13 and got 8.034441857 .....so that works

but how can I get only the previous numbers of Fibonacci in a
specified range from 20 to 20000 if I input a large number like
234.34e10

tia sal2

```

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