On strong uniqueness in linear complex Chebyshev approximation

Discrete linear Chebyshev approximation

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On Reverse Chebyshev Approximation

We investigate the problem of determining the largest domain where given error bounds can be satissed by an approximation of a given continuous real valued real function using polynomials of several kinds. Since the the error bounds are xed and the domain is variable we call this problem reverse Chebyshev approximation.

Real vs Complex Rational Chebyshev Approximation on an Interval

Real VS. Complex Rational Chebyshev Approximation on an Interval

I f f E C[-I, I] is real-valued, let Er( f ) and E'( f ) be the errors in best approximation to f in the supremum norm by rational functions of type ( m , n ) with real and complex coefficients, respectively. It has recently been observed that E'( f ) < Er( f ) can occur for any n > 1, but for no n 1 is it known whether y,,,, = inf, E'( f ) / E r ( f ) is zero or strictly positive. Here we show...

Near-Circularity of the Error Curve In Complex Chebyshev Approximation

Let f(z) be analytic on the unit disk, and let p*(z) be the best (Chebyshev) polynomial approximation to f(z) on the disk of degree at most n. It is observed that in typical problems the “error curve,” the image of the unit circle under (f p*)(z), often approximates to a startling degree a perfect circle with winding number n + 1. This phenomenon is approached by consideration of related proble...