D. Gottlieb et Cw. Shu, ON THE GIBBS PHENOMENON .4. RECOVERING EXPONENTIAL ACCURACY IN A SUBINTERVAL FROM A GEGENBAUER PARTIAL SUM OF A PIECEWISE ANALYTIC-FUNCTION, Mathematics of computation, 64(211), 1995, pp. 1081-1095
We continue our investigation of overcoming the Gibbs phenomenon, i.e,
, to obtain exponential accuracy at all points (including at the disco
ntinuities themselves), from the knowledge of a spectral partial sum o
f a discontinuous but piecewise analytic function. We show that if we
are given the first N Gegenbauer expansion coefficients, based on the
Gegenbauer polynomials C-k(mu)(x) with the weight function (1 - x(2))(
mu-1/2) for any constant mu greater than or equal to 0, of an L(1) fun
ction f(x), we can construct an exponentially convergent approximation
to the point values of f(x) in any subinterval in which the function
is analytic. The proof covers the cases of Chebyshev or Legendre parti
al sums, which are most common in applications.