#10793: Matrices can be "constructed" from matrices of wrong dimensions
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Reporter: vbraun | Owner: jason, was
Type: defect | Status: new
Priority: critical | Milestone: sage-4.6.2
Component: linear algebra | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by jason):
Around line 361 in `matrix/matrix_space.py`, we see:
{{{
if isinstance(entries, (list, tuple)) and len(entries) > 0 and \
sage.modules.free_module_element.is_FreeModuleElement(entries[0]):
#Try to determine whether or not the entries should
#be rows or columns
if rows is None:
#If the matrix is square, default to rows
if self.__ncols == self.__nrows:
rows = True
elif len(entries[0]) == self.__ncols:
rows = True
elif len(entries[0]) == self.__nrows:
rows = False
else:
raise ValueError, "incorrect dimensions"
if self.__is_sparse:
e = {}
zero = self.base_ring()(0)
for i in xrange(len(entries)):
for j, x in entries[i].iteritems():
if x != zero:
if rows:
e[(i,j)] = x
else:
e[(j,i)] = x
entries = e
else:
entries = sum([v.list() for v in entries],[])
}}}
So:
1. I think it tries to be too intelligent about guessing whether you have
rows or columns. That leads to inconsistent behavior when you have code
dealing with different matrix spaces with different dimensions.
2. It indeed does flatten the list if all else fails (that's the
sum([v.list()... line). I agree that that looks dangerous as well.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10793#comment:3>
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