The double description implementation isn't really meant to be used
directly, which is also why it is not by default in the global namespace.
Basically all input must be immutable to be able to use caching. To make an
immutable vector, use:
sage: v = vector([1,2,3])
sage: v.set_immutable()
Immutable means the entries can't be changed any more:
sage: v[0] = 1
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-6-cd90ec5e6613> in <module>()
----> 1 v[Integer(0)] = Integer(1)
/mnt/disk/home/release/Sage/src/sage/modules/vector_integer_dense.pyx in
sage.modules.vector_integer_dense.Vector_integer_dense.__setitem__
(build/cythonized/sage/modules/vector_integer_dense.c:3829)()
183 """
184 if not self._is_mutable:
--> 185 raise ValueError("vector is immutable; please change a
copy instead (use copy())")
186 cdef Integer z
187 cdef Py_ssize_t k, d, n
ValueError: vector is immutable; please change a copy instead (use copy())
On Thursday, March 19, 2015 at 8:28:47 PM UTC+1, Jayant Apte wrote:
>
> Hi
> I was trying to use add_inequality( ) method
> of sage.geometry.polyhedron.double_description.StandardDoubleDescriptionPair
> when I encountered an error (see the MWE below). Upon pulling out the
> functions required for add_inequality( ) and running it seperately, it
> works fine. I wonder if this is a bug or I'm doing something wrong:
>
> sage: from sage.geometry.polyhedron.double_description import
> StandardAlgorithm
> sage: A= matrix([(-1, -1, 0, 0), (-1, 0, 0, 0), (-1, 0, -1, 0), (-1, 0, 0,
> -1)])
> sage: DD, _ = StandardAlgorithm(A).initial_pair()
> sage: ineq=vector([-1, -1, -1, -1])
> sage: DD = DD.add_inequality(ineq);
> sage: print DD
> Double description pair (A, R) defined by
> [-1 -1 0 0]
> [-1 0 0 0] [ 0 0 0 -1 -1 -1]
> A = [-1 0 -1 0], R = [-1 0 0 -1 1 1]
> [-1 0 0 -1] [ 0 -1 0 1 -1 1]
> [-1 -1 -1 -1] [ 0 0 -1 1 1 -1]
> sage: ineq=vector([-1,0,-1,-1])
> sage: DD = DD.add_inequality(ineq);
> ---------------------------------------------------------------------------
> TypeError Traceback (most recent call last)
> <ipython-input-8-d81bd32d70b2> in <module>()
> ----> 1 DD = DD.add_inequality(ineq);
>
> /home/jayant/Software/sagemath6_6/sage/local/lib/python2.7/site-packages/sage/geometry/polyhedron/double_description.pyc
>
> in add_inequality(self, a)
> 681 R_new = []
> 682 for rp, rn in CartesianProduct(R_pos, R_neg):
> --> 683 if not self.are_adjacent(rp, rn):
> 684 continue
> 685 r = a.inner_product(rp) * rn - a.inner_product(rn) * rp
>
> /home/jayant/Software/sagemath6_6/sage/local/lib/python2.7/site-packages/sage/geometry/polyhedron/double_description.pyc
>
> in are_adjacent(self, r1, r2)
> 418 Z_r1 = self.zero_set(r1)
> 419 Z_r2 = self.zero_set(r2)
> --> 420 Z_12 = set(Z_r1).intersection(Z_r2)
> 421 A_Z12 = matrix(self.problem.base_ring(), list(Z_12))
> 422 return A_Z12.rank() == self.problem.dim() - 2
>
> /home/jayant/Software/sagemath6_6/sage/src/sage/modules/vector_integer_dense.pyx
>
> in sage.modules.vector_integer_dense.Vector_integer_dense.__hash__
> (build/cythonized/sage/modules/vector_integer_dense.c:3589)()
> 170 True
> 171 """
> --> 172 return free_module_element.FreeModuleElement.__hash__(self)
> 173
> 174 def __setitem__(self, i, value):
>
> /home/jayant/Software/sagemath6_6/sage/src/sage/modules/free_module_element.pyx
>
> in sage.modules.free_module_element.FreeModuleElement.__hash__
> (build/cythonized/sage/modules/free_module_element.c:7403)()
> 963 """
> 964 if self._is_mutable:
> --> 965 raise TypeError("mutable vectors are unhashable")
> 966 return hash(tuple(self))
> 967
>
> TypeError: mutable vectors are unhashable
>
>
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