[with patch, with 2 positive reviews] sage/modules/free_module_element.pyx computing abs(vector(...))

[mwhansen]

Hi,

It seems the __abs__ method for vectors is missing the part that is
supposed to square the components before they are added.

[e.g. abs(vector([1..5])) should really be
sqrt(1+4+9+16+25)=sqrt(55) ]

The code of the current version is included below.

   def __abs__(self):
       """
       Return the square root of the sum of the squares of the
entries of this vector.

       EXAMPLES:
           sage: v = vector([1..5]); abs(v)
           sqrt(15)
           sage: v = vector(RDF, [1..5]); abs(v)
           3.87298334621
       """
       return sum(self.list()).sqrt()

The last line should be something like

       return sum([x*x for x in self.list()]).sqrt()

(not sure if that is the most efficient way).

--Peter

Component: commutative algebra

Issue created by migration from https://trac.sagemath.org/ticket/1954

[mwhansen]

comment:2

Attachment: 1954.patch.gz

[sagetrac-dmharvey]

comment:5

Looks good to me (I only ran doctests on that file, not on all files).

(If anyone has time, would be good to try doing this without the list call, and also I expect x*x is generally faster than x**2.)

[sagetrac-mabshoff]

comment:7

Merged in Sage 2.10.1.rc2