Hi Volker
I think I understand mutability. What I was wondering was in above MWE,
everything works for the first time I insert an inequality and then the
second time it raises this error.( Did you mean to say I should set the
vectors immutable somewhere inside your code? Just tried setting "ineq"
immutable which doesnt work.)
I want to use DD iteration as a routine in a polyhedral projection
algorithm. Now I could pull out DD iteration code from
double_description.py (have already done so. It works fine. I like the
caching for zero_set.), but if I am to submit the projection code as a
ticket, it would mean duplication of code.
Thanks
On Thursday, 19 March 2015 17:38:49 UTC-4, Volker Braun wrote:
>
> 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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