On Wed, Apr 23, 2014 at 11:31 PM, Kannappan Sampath <kntri...@gmail.com>wrote:
>
>
>
> On Wed, Apr 23, 2014 at 11:19 PM, Vincent Delecroix <
> 20100.delecr...@gmail.com> wrote:
>
>> Me again...
>>
>> If you correct the code, please provide a piece of code that does not
>> work with the current implementation (otherwise, it can not be
>> considered as a bug).
>>
>> Well, OK. My fault. Pass any non-square 0, 1 matrix to it and you would
> see: for example,
>
> IncidenceStructureFromMatrix(Matrix(ZZ, 2, 3, [1]*2*3))
>
>
Sorry, actually: IncidenceStructureFromMatrix(Matrix(ZZ, 3, 2, [1]*2*3))
> If you do correct it please change
>> {{{
>> v = len(M.rows())
>> b = len(M.columns())
>> }}}
>> by
>> {{{
>> v = M.nrows()
>> b = M.ncols()
>> }}}
>>
>>
> Will do!
>
>
>> Best
>> Vincent
>
>
>>
> 2014-04-23 19:42 UTC+02:00, Kannappan Sampath <kntri...@gmail.com>:
>> > :-)
>> >
>> >
>> > On Wed, Apr 23, 2014 at 11:07 PM, Vincent Delecroix <
>> > 20100.delecr...@gmail.com> wrote:
>> >
>> >> What is the problem? You just copy/paste the definition of a function.
>> >>
>> >> 2014-04-23 19:31 UTC+02:00, Kannappan Sampath <kntri...@gmail.com>:
>> >> > Hello group,
>> >> >
>> >> > I think this is probably an embarrassing bug:
>> >> >
>> >> > def IncidenceStructureFromMatrix(M, name=None):
>> >> > """
>> >> > Builds and incidence structure from a matrix.
>> >> >
>> >> > INPUT:
>> >> >
>> >> > - ``M`` -- a binary matrix. Creates a set of "points" from the
>> rows
>> >> and
>> >> > a
>> >> > set of "blocks" from the columns.
>> >> >
>> >> > EXAMPLES::
>> >> >
>> >> > sage: from sage.combinat.designs.block_design import
>> >> > BlockDesign
>> >> > sage: BD1 =
>> >> >
>> BlockDesign(7,[[0,1,2],[0,3,4],[0,5,6],[1,3,5],[1,4,6],[2,3,6],[2,4,5]])
>> >> > sage: M = BD1.incidence_matrix()
>> >> > sage: BD2 = IncidenceStructureFromMatrix(M)
>> >> > sage: BD1 == BD2
>> >> > True
>> >> > """
>> >> > nm = name
>> >> > v = len(M.rows())
>> >> > b = len(M.columns())
>> >> > #points = range(v)
>> >> > blocks = []
>> >> > for i in range(b):
>> >> > B = []
>> >> > for j in range(v):
>> >> > if M[i, j] != 0:
>> >>
>> >
>> > As I tried to explain, the indexing is ballsed up: v is the number of
>> rows,
>> > b is the number of columns. Since i is in range(b), i is a column index
>> and
>> > similarly, j is a row index. So, the code should have looked at M[j, i]
>> as
>> > opposed M[i, j] in the if condition.
>> >
>> > Kannappan.
>> >
>> >> > B.append(j)
>> >> > blocks.append(B)
>> >> > return IncidenceStructure(range(v), blocks, name=nm)
>> >> >
>> >> >
>> >> > The problem is with the indexing "if M[i, j] != 0". Of course, this
>> >> > will
>> >> not
>> >> > be a problem for square 2-designs like the Hadamard design or
>> >> > ProjectivePlaneDesign (thanks to Fisher Type counting), but this
>> should
>> >> > cause problem for designs that are not square. I was bitten by this
>> bug
>> >> when
>> >> > I tried to implement Hadamard 3-design from a Hadamard matrix.
>> >> >
>> >> > I will open a ticket if somebody does a sanity check for me.
>> >> >
>> >> > With Sincere Regards,
>> >> > Kannappan.
>> >> >
>> >> >
>> >> > --
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