I'm refactoring the CDF and RDF matrix code and moving things to numpy.
I ran across the following code in the CDF matrix function
solve_left_LU that handles degenerate cases. This code is supposed to
solve the equation self*x = b and return x.
if self._nrows == 0 or self._ncols == 0:
M=self._column_ambient_module()
return M.zero_vector()
if self._nrows == 0 or self._ncols == 0:
return self.row_module().zero_vector()
The tests provide a use-case:
sage: A = matrix(CDF, 0, 3, [])
sage: A.solve_left_LU(vector(CDF,[]))
()
sage: A = matrix(CDF, 3, 0, [])
sage: A.solve_left_LU(vector(CDF,3, [1,2,3]))
(0, 0, 0)
In the above code, it seems that the second if statement is never
triggered. Should it be triggered sometimes? What is the correct
behavior for a degenerate matrix?
The corresponding code in the RDF case is:
if self._nrows != b.degree():
raise ValueError, "number of rows of self must equal degree
of b"
if self._nrows == 0 or self._ncols == 0:
return self._row_ambient_module().zero_vector()
Giving the following behavior:
sage: A = matrix(RDF, 0, 3, [])
sage: A.solve_left_LU(vector(RDF,[]))
(0.0, 0.0, 0.0)
sage: A = matrix(RDF, 3, 0, [])
sage: A.solve_left_LU(vector(RDF,3, [1,2,3]))
()
Thanks,
Jason
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