Q. about {0,1}-matrices.

[Artur]

Sorry but Title in A125587 is good because matrix is submatrix of themself
but for gracile
Call an nonsingular n X n matrix gracile if all the top left i X i  
submatrices are
singular for all i = 1..n-1.

ARTUR

Dnia 08-01-2007 o 19:34:12 Artur <grafix at csl.pl> napisał(a):

> Dear Jonathan, Neil and Rest of Seqfans,
> In giving these names we have to think yet about next sequence 0 or 1,  
> 2, 40, 584,
> I don't have yet a(5).
> My proposal for these sequence follow Jonatan will be (because these is  
> gracile in comparision with these robust):
> Call an n X n matrix gracile if the top left i X i submatrix is  
> noninvertible for all i = 1..n.
> ARTUR
>
>
> Dnia 08-01-2007 o 18:34:21 Jonathan Post <jvospost3 at gmail.com>  
> napisał(a):
>
>> I suggest a better name for "binary matrices which are not robust":  
>> gracile.
>>
>> A126603 versus A125507.
>>
>> Robust and Gracile are antonyms, used as relative terms in  
>> paleoanthroplogy,
>> generally of bone proportions (i.e., thickness relative to length).
>> Frequently used for Australopithecus, as in "Australopithecus afarensis  
>> and
>> Australopithecus are known as gracile australopithecines, because of  
>> their
>> relatively lighter build, especially in the skull and teeth.  
>> Paranthropus
>> aethiopicus, robustus, and boisei are robust australopithecines."
>
>
>
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I'm not that crazy about the word "gracile".  "Not robust" seems
clearer.

Artur said:

Call an n X n matrix gracile if the top left i X i submatrix is  
noninvertible for all i = 1..n.

that the top left i X i submatrix is  
noninvertible for some i in the range 1..n

Neil