Pythagorean addition

In mathematics, Pythagorean addition is the following binary operation on the real numbers:

The name recalls the Pythagorean theorem, which states that the length of the hypotenuse of a right triangle is ab, where a and b are the lengths of the other sides.

This operation provides a simple notation and terminology when the summands are complicated; for example, the energy-momentum relation in physics becomes

Properties

The operation ⊕ is associative and commutative, and

.

This is enough to form the real numbers into a commutative semigroup. However, ⊕ is not a group operation for the following reasons.

The only element which could potentially act as an identity element is 0, since an identity e must satisfy ee = e. This yields the equation , but if e is nonzero that implies , so e could only be zero. Unfortunately 0 does not work as an identity element after all, since 0⊕(−1) = 1. This does indicate, however, that if the operation ⊕ is restricted to nonnegative real numbers, then 0 does act as an identity. Consequently, the operation ⊕ acting on the nonnegative real numbers forms a commutative monoid.

gollark: No, but it would basically always happen anyway.
gollark: But if it gets flooded times go down, which is great.
gollark: Why even bother with the useless restriction anyway?!
gollark: Probably just forgot to toggle on the `BE_ANNOYING_FOR_NO_REASON` flag somewhere.
gollark: Oh, others can't? Hmm.

See also

Further reading

  • Moler, Cleve and Donald Morrison (1983). "Replacing Square Roots by Pythagorean Sums" (PDF). IBM Journal of Research and Development. 27 (6): 577–581. CiteSeerX 10.1.1.90.5651. doi:10.1147/rd.276.0577..
  • Dubrulle, Augustin A. (1983). "A Class of Numerical Methods for the Computation of Pythagorean Sums" (PDF). IBM Journal of Research and Development. 27 (6): 582–589. CiteSeerX 10.1.1.94.3443. doi:10.1147/rd.276.0582..
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