Can all of the first and second differences of a Costas array be at least 3 in magnitude?











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A Costas array $pi = d_1 d_2 ldots d_n$ (one-line form) of order $n$ is a permutation $pi in S_n$ such that the $n-r$ differences



$d_{r+1} - d_{1} , d_{r+2} - d_{2} , ldots , d_n - d_{n-r}$



are distinct for each $r$ , $1 leq r leq n-1$.



Find an example of a Costas array $pi$ for some $n$ such that the $2n-3$ inequalities



$|d_2 - d_1| , |d_3 - d_2| , ldots , |d_n - d_{n-1}| geq 3$



and



$|d_3 - d_1| , |d_4 - d_2| , ldots , |d_n - d_{n-2}| geq 3$



hold or else prove that no such permutation exists.



Remarks: No such Costas arrays have been found using Beard's database of Costas arrays out to order $1030$ (the database is available at https://ieee-dataport.org/open-access/costas-arrays-and-enumeration-order-1030 and is exhaustive out to order $29$.) Costas arrays are known to exist for infinitely many (but not all) orders by constructions involving the infinitude of primes.










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  • You said $n=11$ doesn't work. What am I missing here: 1 4 7 10 2 5 8 11 3 6 9?
    – Todor Markov
    Nov 26 at 17:15






  • 1




    Ach! I found a flaw in my verification code. Todor Markov your example does work. I am also interested in the same question for the restricted class of permutations known as Costas arrays. I will make the appropriate edits. Thank you.
    – Bill
    Nov 26 at 18:01















up vote
0
down vote

favorite












A Costas array $pi = d_1 d_2 ldots d_n$ (one-line form) of order $n$ is a permutation $pi in S_n$ such that the $n-r$ differences



$d_{r+1} - d_{1} , d_{r+2} - d_{2} , ldots , d_n - d_{n-r}$



are distinct for each $r$ , $1 leq r leq n-1$.



Find an example of a Costas array $pi$ for some $n$ such that the $2n-3$ inequalities



$|d_2 - d_1| , |d_3 - d_2| , ldots , |d_n - d_{n-1}| geq 3$



and



$|d_3 - d_1| , |d_4 - d_2| , ldots , |d_n - d_{n-2}| geq 3$



hold or else prove that no such permutation exists.



Remarks: No such Costas arrays have been found using Beard's database of Costas arrays out to order $1030$ (the database is available at https://ieee-dataport.org/open-access/costas-arrays-and-enumeration-order-1030 and is exhaustive out to order $29$.) Costas arrays are known to exist for infinitely many (but not all) orders by constructions involving the infinitude of primes.










share|cite|improve this question
























  • You said $n=11$ doesn't work. What am I missing here: 1 4 7 10 2 5 8 11 3 6 9?
    – Todor Markov
    Nov 26 at 17:15






  • 1




    Ach! I found a flaw in my verification code. Todor Markov your example does work. I am also interested in the same question for the restricted class of permutations known as Costas arrays. I will make the appropriate edits. Thank you.
    – Bill
    Nov 26 at 18:01













up vote
0
down vote

favorite









up vote
0
down vote

favorite











A Costas array $pi = d_1 d_2 ldots d_n$ (one-line form) of order $n$ is a permutation $pi in S_n$ such that the $n-r$ differences



$d_{r+1} - d_{1} , d_{r+2} - d_{2} , ldots , d_n - d_{n-r}$



are distinct for each $r$ , $1 leq r leq n-1$.



Find an example of a Costas array $pi$ for some $n$ such that the $2n-3$ inequalities



$|d_2 - d_1| , |d_3 - d_2| , ldots , |d_n - d_{n-1}| geq 3$



and



$|d_3 - d_1| , |d_4 - d_2| , ldots , |d_n - d_{n-2}| geq 3$



hold or else prove that no such permutation exists.



Remarks: No such Costas arrays have been found using Beard's database of Costas arrays out to order $1030$ (the database is available at https://ieee-dataport.org/open-access/costas-arrays-and-enumeration-order-1030 and is exhaustive out to order $29$.) Costas arrays are known to exist for infinitely many (but not all) orders by constructions involving the infinitude of primes.










share|cite|improve this question















A Costas array $pi = d_1 d_2 ldots d_n$ (one-line form) of order $n$ is a permutation $pi in S_n$ such that the $n-r$ differences



$d_{r+1} - d_{1} , d_{r+2} - d_{2} , ldots , d_n - d_{n-r}$



are distinct for each $r$ , $1 leq r leq n-1$.



Find an example of a Costas array $pi$ for some $n$ such that the $2n-3$ inequalities



$|d_2 - d_1| , |d_3 - d_2| , ldots , |d_n - d_{n-1}| geq 3$



and



$|d_3 - d_1| , |d_4 - d_2| , ldots , |d_n - d_{n-2}| geq 3$



hold or else prove that no such permutation exists.



Remarks: No such Costas arrays have been found using Beard's database of Costas arrays out to order $1030$ (the database is available at https://ieee-dataport.org/open-access/costas-arrays-and-enumeration-order-1030 and is exhaustive out to order $29$.) Costas arrays are known to exist for infinitely many (but not all) orders by constructions involving the infinitude of primes.







combinatorics discrete-mathematics permutations






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edited Nov 26 at 18:29

























asked Nov 26 at 16:58









Bill

294




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  • You said $n=11$ doesn't work. What am I missing here: 1 4 7 10 2 5 8 11 3 6 9?
    – Todor Markov
    Nov 26 at 17:15






  • 1




    Ach! I found a flaw in my verification code. Todor Markov your example does work. I am also interested in the same question for the restricted class of permutations known as Costas arrays. I will make the appropriate edits. Thank you.
    – Bill
    Nov 26 at 18:01


















  • You said $n=11$ doesn't work. What am I missing here: 1 4 7 10 2 5 8 11 3 6 9?
    – Todor Markov
    Nov 26 at 17:15






  • 1




    Ach! I found a flaw in my verification code. Todor Markov your example does work. I am also interested in the same question for the restricted class of permutations known as Costas arrays. I will make the appropriate edits. Thank you.
    – Bill
    Nov 26 at 18:01
















You said $n=11$ doesn't work. What am I missing here: 1 4 7 10 2 5 8 11 3 6 9?
– Todor Markov
Nov 26 at 17:15




You said $n=11$ doesn't work. What am I missing here: 1 4 7 10 2 5 8 11 3 6 9?
– Todor Markov
Nov 26 at 17:15




1




1




Ach! I found a flaw in my verification code. Todor Markov your example does work. I am also interested in the same question for the restricted class of permutations known as Costas arrays. I will make the appropriate edits. Thank you.
– Bill
Nov 26 at 18:01




Ach! I found a flaw in my verification code. Todor Markov your example does work. I am also interested in the same question for the restricted class of permutations known as Costas arrays. I will make the appropriate edits. Thank you.
– Bill
Nov 26 at 18:01















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