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March 9th, 2019, 10:24 AM   #1
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Reverse Fibonacci series.

Reference :

https://www.programiz.com/c-programm...bonacci-series

Can we write a computer program which
will print reverse Fibonacci series numbers starting
from 100 till 0?

The computer program could be in any
programming language viz C,C++,Java,C#, Python etc.

Thanks & Regards,
Prashant S Akerkar

Last edited by akerkarprash; March 9th, 2019 at 10:25 AM. Reason: Content updates
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March 9th, 2019, 10:34 AM   #2
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Math Focus: Wibbly wobbly timey-wimey stuff.
Quote:
Originally Posted by akerkarprash View Post
Reference :

https://www.programiz.com/c-programm...bonacci-series

Can we write a computer program which
will print reverse Fibonacci series numbers starting
from 100 till 0?

The computer program could be in any
programming language viz C,C++,Java,C#, Python etc.

Thanks & Regards,
Prashant S Akerkar
Why are you asking these? Someone gave you a method of printing the numbers in a list backward in another thread. Are you actually asking about Fibonacci numbers rather than programming?

-Dan
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March 9th, 2019, 10:40 AM   #3
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/* generate the Fibonacci series to a list or array */
a[1]=1;a[2]=1;

for(i=3,i<=100,i++){
a[i]=[i-1]+a[i-2];
}

/* read out the array backwards */
for (i=100,i>=1,i--) {
printf("%d\n",a[i]);
}

That might be valid C (it's been decades) but it's better interpreted as pseudocode.

Another method involves knowing $F_{100},~F_{99}$ ahead of time. Then you can do

a[100]=$F_{100}$;
a[99]=$F_{99}$;
for (i=98,i>=1,i--){
a[i] = a[i+2]-a[i+1];
}
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March 9th, 2019, 10:41 AM   #4
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The number 100 isn't a Fibonacci number. It wasn't clear what was meant. However, individual Fibonacci numbers are easily calculated.

Last edited by skipjack; March 9th, 2019 at 11:10 AM.
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March 9th, 2019, 10:44 AM   #5
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Thanks.

https://www.programiz.com/c-programm...bonacci-series

I want to trace the programming logic
for printing the Fibonacci series in reverse order.

Can we can term this new series as
Reverse Fibonacci numbers series?

Thanks & Regards,
Prashant S Akerkar
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March 9th, 2019, 10:56 AM   #6
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Starting with which Fibonacci number?

Fibonacci numbers can be quite large, so the languages you've mentioned might not be good choices.
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March 9th, 2019, 10:59 AM   #7
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Thanks.

I feel we should start with 89 till 0 for printing Reverse Fibonacci numbers series.

Next Fibonacci number after 89 is 144 which is greater than 100.

Thanks & Regards,
Prashant S Akerkar
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March 9th, 2019, 03:19 PM   #8
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Ye olde UBasic again:

u=89
v=55
DOWHILE v>0
PRINT u,
w=u-v
u=v
v=w
ENDDO

Output:
89,55,34,21,13,8,5,3,2,1,1
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March 9th, 2019, 05:38 PM   #9
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Quote:
Originally Posted by Denis View Post
Ye olde UBasic again:

u=89
In order to find the right value of u you had to compute the Fibs forward. This is actually a harder and more interesting situation than the primes. How do you determine the largest Fib number less than some given value?

There turns out to be a closed-form expression for the n-th Fib, you could use that.

A Closed Form of the Fibonacci Sequence - Mathonline
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March 9th, 2019, 07:31 PM   #10
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If going back from 100, you could just write a sentence of the numbers as text... which I suppose is generally true of any finite initial segment written backwards. Calculating it isn’t hard either as noted above. So long as your calculation of an initial and each successive Fib. is one that can be done in a finite number of steps, and in this case it most certainly is, there is a formula for it.
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