toms886, an Octave code which implements an interpolation procedure based on "Padua points", defined in the square [-1,+1]^2, whose interpolating power is especially good. It is possible to map these points to the general rectangle, ellipse or triangle to do interpolation on these regions as well.
The text of many ACM TOMS algorithms is available online through ACM: https://calgo.acm.org/ or NETLIB: https://www.netlib.org/toms/index.html.
The computer code and data files made available on this web page are distributed under the MIT license
toms886 is available in a C version and a C++ version and a Fortran90 version and a MATLAB version and an Octave version.
lagrange_interp_2d, an Octave code which defines and evaluates the lagrange polynomial p(x,y) which interpolates a set of data depending on a 2d argument that was evaluated on a product grid, so that p(x(i),y(j)) = z(i,j).
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Marco Caliari, Stefano de Marchi, Marco Vianello.