I experience a weird effect of @parallel
decorator.
Let's consider an example of FiniteMonoidFromMultiplicationTable
defined in https://ask.sagemath.org/question/32064/
I define this monoid and a list of three its elements and compute their product as follows:
F = FiniteMonoidFromMultiplicationTable([[0, 0, 0], [0, 1, 1], [0, 1, 2]])
E1 = [ F(0), F(1), F(2) ]
print('product1:', prod(E1) )
It prints product1: 0
. So far good.
Now let's define the parallel id
function that simply returns its argument, and apply it (in parallel fashion) to E1
to obtain list E2
as follows:
@parallel
def id(x):
return x
E2 = [ e for _,e in id(E1) ]
print('product2:', prod(E2) )
However, prod(E2)
here results in the error
TypeError: unsupported operand parent(s) for *: 'Finite monoid on 3 elements given by its multiplication table' and 'Finite monoid on 3 elements given by its multiplication table'
which is rather weird. While E2[0].parent() == E2[1].parent()
evaluates to True
here, E2[0].parent() is E2[1].parent()
evaluates to False
and that's probably the cause for the error above.
So, my questions are: why elements of E2
have different parents and what needs to be changed to avoid the described issue?
PS. Just in case, here is the full code at Sagecell illustrating the issue.