Status: Valid
Owner: ----
Labels: Type-Defect Priority-Medium Matrices
New issue 3401 by [email protected]: Slicing an empty matrix is broken
http://code.google.com/p/sympy/issues/detail?id=3401
This used to work:
In [4]: Matrix(0, 3, [])[:, 0]
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
<ipython-input-4-4596a324e212> in <module>()
----> 1 Matrix(0, 3, [])[:, 0]
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/matrices/matrices.py
in __getitem__(self, key)
286 i, j = key
287 if type(i) is slice or type(j) is slice:
--> 288 return self.submatrix(key)
289
290 else:
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/matrices/matrices.py
in submatrix(self, keys)
1022 extract
1023 """
-> 1024 rlo, rhi, clo, chi = self.key2bounds(keys)
1025 outLines, outCols = rhi-rlo, chi-clo
1026 outMat = [0]*outLines*outCols
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/matrices/matrices.py
in key2bounds(self, keys)
1097 clo, chi = self.slice2bounds(keys[1], self.cols)
1098 else:
-> 1099 _, clo = self.slice2bounds((0, keys[1]), self.cols)
1100 chi = clo + 1
1101 if not ( 0<=rlo<=rhi and 0<=clo<=chi ):
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/matrices/matrices.py
in slice2bounds(self, key, defmax)
1138 elif isinstance(key, tuple):
1139 key = [defmax - 1 if i == -1 else i for i in key]
-> 1140 return self.key2ij(key)
1141 else:
1142 raise IndexError("Improper index type")
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/matrices/matrices.py
in key2ij(self, key)
1120 i, j = [(k + n) if k < 0 else k for k, n in zip(key,
(self.rows, self.cols))]
1121 if not (i>=0 and i<self.rows and j>=0 and j < self.cols):
-> 1122 raise IndexError("Index out of range: a[%s]"%repr(key))
1123 return i,j
1124
IndexError: Index out of range: a[[0, 0]]
It was broken by the commit
commit d8e586b4debff9ac51a9fd7ea59b298ce6bfad40
Author: Chris Smith <[email protected]>
Date: Wed Nov 30 14:55:40 2011 +0545
key2ij is used rather than slice to resolve int indices
The key2ij routine is also moved closer to the functions that use
it.
Factor out key2bounds code in matrices, too.
The problem is that the internal routines convert the first : to a range of
0 to 0, which is wrong (it should have no range). It then tests 0 <= 0 <
0, which gives False.
It's not clear how this should be fixed, though. There are four functions
in matrices.py involved here: __getitem__, key2bounds, key2ij, and
slice2bounds. It's not clear in which of these functions the change should
go, or what it should look like. They all seem to operate on a core
assumption that any slice can be represented by a range, which is not true
in this case as I said.
This is causing a test failure in pull request 1530.
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