Positive Roots and Simple Roots
Given a root system Φ we can always choose (in many ways) a set of positive roots. This is a subset of Φ such that
- For each root exactly one of the roots, – is contained in .
- For any two distinct such that is a root, .
If a set of positive roots is chosen, elements of are called negative roots.
An element of is called a simple root if it cannot be written as the sum of two elements of . The set of simple roots is a basis of with the property that every vector in is a linear combination of elements of with all coefficients non-negative, or all coefficients non-positive. For each choice of positive roots, the corresponding set of simple roots is the unique set of roots such that the positive roots are exactly those that can be expressed as a combination of them with non-negative coefficients, and such that these combinations are unique.
Read more about this topic: Root System
Famous quotes containing the words positive, roots and/or simple:
“Nurturing competence, the food of self-esteem, comes from acknowledging and appreciating the positive contributions your children make. By catching our kids doing things right, we bring out the good that is already there.”
—Stephanie Martson (20th century)
“Einstein is not ... merely an artist in his moments of leisure and play, as a great statesman may play golf or a great soldier grow orchids. He retains the same attitude in the whole of his work. He traces science to its roots in emotion, which is exactly where art is also rooted.”
—Havelock Ellis (1859–1939)
“All propaganda or popularization involves a putting of the complex into the simple, but such a move is instantly deconstructive. For if the complex can be put into the simple, then it cannot be as complex as it seemed in the first place; and if the simple can be an adequate medium of such complexity, then it cannot after all be as simple as all that.”
—Terry Eagleton (b. 1943)