Recursive sequences in CAS on prime.

06192015, 07:22 AM
Post: #1




Recursive sequences in CAS on prime.
Hello
I can't figure out how to define a recursive sequence in CAS on the HP prime. I want to define: u(1)=3/2 u(2)=5/3 u(n)=20036002/u(n1)+4000/(u(n1)u(n2)) Of course, I can define this sequence in the sequence app in HOME mode but it gives wrong answers (the sequence is made for that purpose ) so I want to have exact values in CAS. I made a CAS program with a FOR loop and it works fine but I'm looking for a more straightforward way to do this. In XCAS, I can type in Code: u(n):={si n==1 alors 3/2; sinon si n==2 alors 5/3; sinon 20036002/u(n1)+4000/(u(n1)*u(n2)); fsi; fsi;} I am looking for a similar syntax working on the prime too. thank you for your help. 

06192015, 09:01 AM
Post: #2




RE: Recursive sequences in CAS on prime.
Here is a solution:
Code: #cas Arno 

06192015, 09:20 AM
Post: #3




RE: Recursive sequences in CAS on prime.
Thank you. This is a way to do this. But is there another way, without making a CAS program ? with a declaration like u(n):= ... ?


06192015, 10:33 AM
Post: #4




RE: Recursive sequences in CAS on prime.
Hello Arne,
maybe your program runs faster, if you create two local variables, wich get the values of mf(n1) and mf(n2), so you have to do the recursive call only twice ind not three times. regards Wolfgang 

06192015, 02:12 PM
Post: #5




RE: Recursive sequences in CAS on prime.
(06192015 10:33 AM)ww63 Wrote: Hello Arne, Yes, you are right, a reduction of recursive calls is necessary. But your solution, I think, will not work with local variables as they are created each time when the function is called. Here additional Parameters are necessary to pass the last two values and then the solution with a forloop seems better. Arno 

06192015, 04:37 PM
Post: #6




RE: Recursive sequences in CAS on prime.
I managed to declare the sequence directly in CAS:
Code: u:=(n)>CASE IF (n==1) THEN 3/2 END IF (n==2) THEN 5/3 END IF n>2 THEN 20036002/u(n1)+4000/(u(n1)*u(n2)) END END It works fine until n>10. After this, the recursion is too deep. I made a CAS program too with a FOR loop : Code:
But after all this, I think my favorite method is to use the spreadsheet with cells in CAS mode. It is fast and quite easy. 

« Next Oldest  Next Newest »

User(s) browsing this thread: 1 Guest(s)