An idempotent semifield is an idempotent semiring that has a zero and in which every non-zero element is invertible. Or, in other words, a skewfield in which an element may not have a negative but is always idempotent with respect to addition.
An idempotent semifield is idempotent semiring that has a zero and in which for every non-zero element there is an element such that . It is said to be commutative if the multiplication is commutative.
As in the case of an idempotent semiring there is a partial order given by
which has a join given by addition. In case of an idempotent semifield this partial order also has a meet. To each semifield there is a dual semifield given on the same set of elements as and with the same zero, identity, and multiplication but with addition given by interchanging join and meet, i.e. the meet becomes the new addition on non-zero elements and the zero element behaves neutral.
A version of the fundamental theorem of algebra can be formulated for semifields: A semifield is said to be algebraically closed if the equation has a solution for all and .
In an algebraically closed commutative idempotent semifield with for all the equation
with and has a solution in if and only if . If , then the solution is unique and can be expressed in terms of the coefficients with help of radicals, multiplication, inverse and meet (i.e. a polynomial in the radicals of over the dual semifield).
The max-plus algebra with addition given by maximum and multiplication given by ordinary addition.
The two element semifield with and is commutative and algebraically closed but does not fulfill the assumptions of theorem . Indeed, the equation does not have a unique solution.
In the reference the assumption that is not explicit (otherwise the base step in the induction in the proof of Proposition 2 therein doesn’t work).
Last revised on July 12, 2021 at 11:18:55. See the history of this page for a list of all contributions to it.