Download Fibonacci Numbers and Binet Formula (An Introduction to Number

Fibonacci Numbers
and Binet Formula
(An Introduction to
Number Theory)
By:
(The Ladies)
2
Recurrence Sequence
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each further term of the sequence is defined as a
function of the preceding terms (starting seed and rule)
Fibonacci sequence
(1,1,2,3,5,8,13,21,34,55...)
Lucas sequence
(2,1,3,4,7,11,18,29,47,76)
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take 3+8
(1+2)+(3+5)
(1+3)+(2+5)
(4)+(7) - can be shown to hold in general
Mathematical induction
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Fibonacci (1,1,2,3,5,8,13...)
1,1+1,1+1+2,1+1+2+3,1+1+2+3+5,1+1+2+3+5+8...
1,2,4,7,12,20...
+1 to each term
2,3,5,8,13,21...
because 1+1+2+3+5+8
1+1+1+2+3+5+8
(2+1)+2+3+5+8
(3+2)+3+5+8
(5+3)+5+8
(8+5)+8
Fibonacci sequence patterns
Fibonacci (1,1,2,3,5,8,13...)
neither arithmetic nor geometric
so write it in a different way
1/1=1
2/1=(1+1)/1 = (1+(1/1))
3/2=(2+1)/2=1+(1/2)= 1+ 1/(1+(1/1))
5/3=(3+2)/3=1+(2/3)=1+ 1/(1+ 1/(1+(1/1)))
and so on
(Golden ratio φ)
Golden Ratio φ
φ=1+1/φ
φ2=φ+1 quadratic equation
φ=(1+sqrt(5))/2 (only the positive
answer)
φ=1.618033989...
Golden Ratio and practical
application
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most famous and controversial in history human aesthetics
Converting between km and miles
1 mile= 1.6093 km
13 km = 8 miles
Fibonacci (1,1,2,3,5,8,13,21...)
OK, using Fibonacci numbers, how many
miles are in 50 kilometers?? (show your
work)
Binet Formula
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A formula to find a term in a Fibonacci numbers without
generating previous terms
Jacques Binet in 1843 - known to Euler and Bernoulli
100 years before
Fibonacci numbers are actually a combo of two
geometric progressions
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Recall φ2=φ+1 and τ2=τ+1 identities
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Use them to come up with a formula for the Fibonacci
Binet Formula
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φ2=φ+1 and τ2=τ+1 identities
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φ2= φ+1
φ3=φ(φ2)=φ(φ+1)=(φ2)+φ=(φ+1)+φ= 2φ+1
φ4=φ(φ3)=φ(2φ+1)=(2φ2)+φ=2(φ+1)+φ= 3φ+2
φ5=φ(φ4)=φ(3φ+2)=(3φ2)+2φ=3(φ+1)+2φ= 5φ+3
φ6=φ(φ5)=φ(5φ+3)=(5φ2)+3φ=5(φ+1)+3φ= 8φ+5
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φ2=1φ+1
φ3=2φ+1
φ4=3φ+2
φ5=5φ+3
So, φn=Fnφ+Fn-1
and
τn=Fnτ+Fn-1
Binet Formula
φ^n=Fnφ+Fn-1
τ^n=Fnτ+Fn-1
φ^n - τ^n=Fnφ - Fnτ
Fn= (φ^n - τ^n) / (φ - τ)
remember that φ = (1+sqrt(5))/2 and τ = (1+sqrt(5))/2
therefore (φ - τ) = sqrt (5)
Fn= (φ^n - τ^n) / sqrt(5)
Fn=(φ^n/sqrt(5)) - (τ^n/sqrt(5)) (two geometric progressions)
now for the Fibonacci term 1000 is
F1000= (φ^(10000) - τ^(10000)) / sqrt(5) = 43466557686937456... (209 digits)
The Fibonacci Sequence in Nature
http://www.youtube.com/watch?v=ahXIMUkSX
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Application : The Towers of Hanoi
The Rules:
From here:
To here:
Without:
1. Moving more than one disk at a time.
2. Placing a larger disk on top of a smaller disk.
An Example:
1
3
5
2
4
6
7
The Goal:
To find the minimum number of moves
necessary to complete the puzzle.
hn = # of moves required to transfer n disks.
Let us find a recurrence rule to predict hn.
What We Know:
h3 = 7
h7 = 123
h4 = 15
= 247
h5 = 31
h6 = 63
hn = small disks + big disk + small disks
hn-1
2hn-1
+1
+1
+ hn-1
h8
Closed Formula:
3, 7, 15, 31, 63, ...
One less than a power of 2?
3 = 22 - 1
7 = 23 - 1
15 = 24 - 1
hn = 2n -1
Prediction : End of the World?
High on the mountaintops sat a monk who
could foretell the end of the world. He had a
Tower of Hanoi with 64 gleaming diamond
disks and could move one a second. When
he stopped the world would end.
How long do we have?
Prediction : Solution
Number of moves required 264 -1
So . . .
roughly 583,344,214,028 years.
Prime Numbers: How do we find them?
200 B.C. Eratosthenes invented the sieve.
Prime Numbers:
Prime Numbers:
Prime Numbers:
Prime Numbers:
Prime Numbers:
And it stops.
Why?
The number of tests is the
# of primes < testing maximum
Proof by contradiction:
1. A composite exists in 11-100
2. Thus, it is not a multiple of a P < 10
3. Thus, both factors > 10
4. Therefore, the composite > 100
Prime Numbers: How many exist?
E = P1 * P2 * P3 * P4 ... Pn
now...
q = P1 * P2 * P3 * P4 * ... * Pn + 1
Following the Composite Theorems (must be
factor of unique prime numbers), infinite
prime numbers exist.
Where Aren't the Prime Numbers?
2*3 + 2 = composite
composite
2*3 + 3 =
K = 2 * 3 * 4 * ... * (N+1)
K+2 = 2 * 3 * 4 * ... * (N+1) +2
K+3 = 2 * 3 * 4 * ... * (N+1) + 3
K+(N+1) = 2 * 3 * 4 * ... * (N+1) + (N+1)
K+2, K+3, K+4, K+(N+1) --> all composite,