Bill Allombert on Wed, 02 Mar 2016 18:52:53 +0100 |
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Re: extremal case of component extraction |
On Mon, May 20, 2013 at 05:08:23PM +0200, Bill Allombert wrote: > Dear PARI developers, > > In PARI 2.6.0 we have: > > ? [1,2][2..-2] > *** at top-level: [1,2][2..-2] > *** ^------------ > *** _[_.._]: inconsistent dimensions in _[..]. > > ? [1,2][2..1] > *** at top-level: [1,2][2..1] > *** ^----------- > *** _[_.._]: inconsistent dimensions in _[..]. > > I think a case could be made to return [] in both case. > > On the other hand > > ? [1,2][3..1] > > should probably fail. I implement that. Also 0 is handled differently. Specifically: 1. Negative values are converted to positive value by adding the length. 2. 0 is considered negative when at the left of "..", positive otherwise 3. [a..b] is allowed as long as (after the above conversion) b-a+1 >= 0 and return a vector of length b-a+1. So V[1..0] and V[0..-1] returns []. Cheers, Bill.