hey list,
If you look at the code, there is a function called _new_c() which is
used in the multiplication algorithm.
In there, the following line is called:
x = Matrix_integer_2x2.__new__(Matrix_integer_2x2,
self._parent, None, False, False)
this returns a Matrix_integer_2x2, but is different from the one you
get, if you call:
Matrix_integer_2x2(M2Z,None,false,false)
sage: from sage.matrix.matrix_integer_2x2 import Matrix_integer_2x2 as mi2x2
sage: M2Z = MatrixSpace(ZZ,2)
sage: null = mi2x2(M2Z,None,false,false);null
[0 0]
[0 0]
sage: some_other_null = mi2x2.__new__(mi2x2, M2Z , None, False,
False);some_other_null
[]
sage: some_other_null.set_immutable()
---
AttributeError Traceback (most recent call last):
[..]
AttributeError: 'NoneType' object has no attribute 'set_immutable'
even, if in _new_c the number of cols and rows is set, I think there is
some internal object, which still has no value
greatz Johannes
On 10.01.2013 10:10, David Loeffler wrote:
> The following curious bug came up during work on ticket #12233. For some
> reason, if one creates a 2x2 integer matrix directly using the
> constructor then it is possible to tell it to be immutable; but if one
> creates one via arithmetic operations then calling "set_immutable" on it
> fails. Here's an example:
>
> sage: from sage.matrix.matrix_integer_2x2 import Matrix_integer_2x2 as
> mi2x2
> sage: M2Z = MatrixSpace(ZZ,2)
> sage: mi2x2(M2Z, [1,0,0,1])
> sage: x=mi2x2(M2Z, [1,0,0,1], false, false)
> sage: y=mi2x2(M2Z, [1,0,0,1], false, false)
> sage: type(x)
>
> sage: z = x*y
> sage: type(z)
>
> sage: x.set_immutable()# ok
> sage: z.set_immutable()# error
> [...]
> AttributeError: 'NoneType' object has no attribute 'set_immutable'
>
> (Many thanks to Timo Kluck for clarifying the problem and finding this
> example.) Does anyone have any idea what's going on here, and if so how
> to fix it?
>
> Regards, David
>
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