On Apr 4, 2011, at 15:19 , John H Palmieri wrote:
> On Monday, April 4, 2011 3:00:20 PM UTC-7, pong wrote:
>>
>> By that I simply mean a function that on input a real matrix M returns
>> the matrix N such that n[i][j] = abs(m[i][j]).
>>
>> This can be achieve by something like:
>>
>> n = len(M.rows()); m =len(M.columns()); N = matrix(n,m,lambda i,j:
>> abs(M[i][j]));
>>
>> However, for a square matrix M, M.abs() returns something which wasn't
>> what one expected:
>>
>> B = matrix(2,2,lambda i,j: i-j); B; B.abs()
>>
>> returns
>>
>> [ 0 -1]
>> [ 1 0]
>>
>> and 1
>>
>> Is it a bug? Or something that I missed?
>>
>
> For matrices, B.abs() returns the determinant. If you type "B.abs?", you'll
> see a message like
>
> Return the absolute value of self. (This just calls the __abs__
> method, so it is equivalent to the abs() built-in function.)
>
> Then if you type "B.__abs__?", you'll see
>
> Synonym for self.determinant(...).
I suppose this is because the determinant is sometimes written as
|1 0|
|0 -1|
but I think that's carrying things too far. I'd say this violates the
Principle of Least Surprise...
I see two "bugs": that introspection claims that ".abs()" is defined in the
file it claims:
=======================
sage: B.abs?
String Form: <built-in method abs of
sage.matrix.matrix_integer_dense.Matrix_integer_dense object at 0x10ce3a4d0>
Namespace: Interactive
Definition: B.abs(self)
Docstring:
Return the absolute value of self. (This just calls the __abs__
method, so it is equivalent to the abs() built-in function.)
=======================
(which is not the case); and the use of "abs" (in any form) for determinant.
But that's just me.
Justin
--
Justin C. Walker
Curmudgeon-at-large
Director
Institute for the Absorption of Federal Funds
----
186,000 Miles per Second
Not just a good idea:
it's the law!
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