We study AAK-type meromorphic approximants to functions of the form F (z) = Z dλ(t) z − t +R(z), where R is a rational function and λ is a complex measure with compact regular support included in (−1, 1), whose argument has bounded variation on the support. The approximation is understood in L-norm of the unit circle, p ≥ 2. We dwell on the fact that the denominators of such approximants satisf...

We investigate the approximation of some hypergeometric functions of two variables, namely the Appell functions Fi, i = 1, . . . , 4, by multivariate Padé approximants. Section 1 reviews the results that exist for the projection of the Fi onto x = 0 or y = 0, namely, the Gauss function 2F1(a, b; c; z), since a great deal is known about Padé approximants for this hypergeometric series. Section 2...

We study diagonal multipoint Padé approximants to functions of the form F (z) = Z dλ(t) z − t +R(z), where R is a rational function and λ is a complex measure with compact regular support included in R, whose argument has bounded variation on the support. Assuming that interpolation sets are such that their normalized counting measures converge sufficiently fast in the weak-star sense to some c...

Pad6 approximants are a frequently used tool for the solution of mathematical problems. One of the main drawbacks of their use for multivariate functions is the calculation of the derivatives of f ( x 1 .... ,xp). Therefore multivariate Newton-Pad6 approximants are introduced; their computation will only use the value of f at some points. In Sect. 1 we shall repeat the univariate Newton-Pad6 ap...

In this work we compare semi-discrete formulations to obtain numerical solutions for the 1D Burgers equation. The formulations consist in the discretization of the time-domain via multi-stage methods of second and fourth order: R11 and R22 Padé approximants, and of the spatial-domain via finite element methods: least-squares (MEFMQ), Galerkin (MEFG) and Streamline-Upwind Petrov-Galerkin (SUPG)....

The usual way to compute a low-rank approximant of a matrix H is to take its singular value decomposition (SVD) and truncate it by setting the small singular values equal to 0. However, the SVD is computationally expensive. This paper describes a much simpler generalized Schur-type algorithm to compute similar low-rank approximants. For a given matrix H which has d singular values larger than ε...

The usual way to compute a low-rank approximant of a matrix H is to take its singular value decomposition (SVD) and truncate it by setting the small singular values equal to 0. However, the SVD is computationally expensive. This paper describes a much simpler generalized Schur-type algorithm to compute similar low-rank approximants. For a given matrix H which has d singular values larger than ε...

Abstract. This paper is devoted to the study of asymptotic zero distribution of Laurent-type approximants under certain extremality conditions analogous to the condition of Grothmann [1], which can be traced back to Walsh’s theory of exact harmonic majorants [8, 9]. We also prove results on the convergence of ray sequences of Laurent-type approximants to a function analytic on the closure of a ...

By means of atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, we found three types of giant approximants of decagonal quasicrystal in Al-Cr-Fe-Si alloys, where each type contains several structural variants possessing the same lattice parameters but different crystal structures. The projected structures of these approximants along the pseudo-tenfold dire...

A trial application of the method of Feynman-Kleinert approximants is made to perturbation series arising in connection with the lattice Schwinger model. In extrapolating the lattice strong-coupling series to the weak-coupling continuum limit, the approximants do not converge well. In interpolating between the continuum perturbation series at large fermion mass and small fermion mass, however, ...