Max-plus algebra

Max-plus algebra

A max-plus algebra is an algebra over the real numbers with maximum and addition as the two binary operations. It can be used appropriately to determine marking times within a given Petri net and a vector filled with marking state at the beginning.

Contents

Operators

Scalar operations

Let A and B be scalars. Then the operations maximum (implied by the max operator  \oplus) and addition (plus operator  \otimes) for this scalars are defined as

A \oplus B = \max(A,B)
A \otimes B = A + B

Watch: Max-operator \oplus can easily be confused with the addition operation. All \otimes - operations have a higher precedence than \oplus - operations.

Matrix operations

Max-Plus algebra can be used for matrix operands M, N likewise. To perform the R = M \oplus N - operation, the elements of the resulting matrix R (row i, column j) have to be set up by the maximum operation of both corresponding elements of the matrices M and N:

Rij = Mij \oplus Nij

The  \otimes - operation is similar to algorithm of Matrix multiplication, however, every "+" calculation has to be substituted by a \oplus - operation, every "\cdot" calculation by a \otimes - operation.

Useful enhancement elements

In order to handle marking times like -\infty which means "never before", the ε-element has been established by ε=-\infty. According to the idea of infinity, the following equations can be found:

ε \oplus A = A
ε \otimes A = ε

To point the zero number out, the element e was defined by e = 0. Therefore:

e \otimes A = A

Obviously, ε is the neutral element for the \oplus - operation as well as e is for the \otimes - operation

Algebra properties

  • associativity:
(A \oplus B) \oplus C = A \oplus (B \oplus C)
(A\otimes B) \otimes C = A \otimes (B \otimes C)
  • commutativity :
A \oplus B = B \oplus A
  • distributivity:
 (A \oplus B) \otimes C = A \otimes C \oplus B \otimes C

Note: In general, A \otimes B = B \otimes A does not hold, for example in the case of matrix operations.

See also

Additional reading

  • Butkovič, Peter (2010), Max-linear Systems: Theory and Algorithms, Springer Monographs in Mathematics, Springer-Verlag, doi:10.1007/978-1-84996-299-5 

External links