Diophantine Approximation - Measure of The Accuracy of Approximations

Measure of The Accuracy of Approximations

The obvious measure of the accuracy of a Diophantine approximation of a real number α by a rational number p/q is However, this quantity may always be made arbitrarily small by increasing the absolute values of p and q; thus the accuracy of the approximation is usually estimated by comparing this quantity to some function φ of the denominator q, typically a negative power of it.

For such a comparison, one may want upper bounds or lower bounds of the accuracy. A lower bound is typically described by a theorem like "for every element α of some subset of the real numbers and every rational number p/q, we have ". In some case, "every rational number" may be replaced by "all rational numbers except a finite number of them", which amounts to multiplying φ by some constant depending on α.

For upper bounds, one has to take into accounts that not all the "best" Diophantine approximations provided by the convergents may have the desired accuracy. Therefore the theorems take the form "for every element α of some subset of the real numbers, there are infinitely many rational numbers p/q such that ".

Read more about this topic:  Diophantine Approximation

Famous quotes containing the words measure of the, measure of, measure and/or accuracy:

    The measure of the little while
    That I’ve been long away.
    Robert Frost (1874–1963)

    Might was the measure of right.
    Marcus Annaeus Lucan (39–65)

    The gifts he gave were that some would be apostles, some prophets, some evangelists, some pastors and teachers, to equip the saints for the work of ministry, for building up the body of Christ, until all of us come to the unity of the faith and of the knowledge of the Son of God, to maturity, to the measure of the full stature of Christ.
    Bible: New Testament, Ephesians 4:11.

    As for farming, I am convinced that my genius dates from an older era than the agricultural. I would at least strike my spade into the earth with such careless freedom but accuracy as the woodpecker his bill into a tree.
    Henry David Thoreau (1817–1862)