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function r = poly2ac(a,efinal)
// Convert prediction polynomial to autocorrelation sequence.
//Run rlevinson.sci before running this
// Calling Sequence
// R = poly2ac(a,efinal)
//
// Parameters
// a: input prediction polynomial with 1st element 1 (if not, poly2ac normalizes it to 1 before proceeding).
// efinal: input prediction error
// r: output autocorrelation sequence
//
// Description
// This function obtains the underlying autocorrelation sequence that would best fit a linear prediction filter described by the
// denominator polynomial and the numerator scaling. The filter is H(z) = efinal/(a(1) + a(2) x z a(3) x z^2 ... a(n) x z^n-1)
//
// Examples
// a = [1.0000 0.4288 0.76 0.0404 -0.02];
// efinal = 0.2; // Step prediction error
// r = poly2ac(a,efinal) // Autocorrelation sequence
//
// See also
// ac2poly
// poly2rc
// rc2poly
// rc2ac
// ac2rc
//
// Author: Parthe Pandit
//
// Bibliography
// S. Kay, Modern Spectral Estimation, Prentice Hall, N.J., 1987, Chapter 6.
//errcheck 1: Check for input format of polynomial
if (size(a,1) > 1 & size(a,2) > 1) then
error("Input polynomial has to be a 1-dimensional array")
end
if (length(efinal) > 1) then
error("Input efinal has to be a scalar")
end
r = rlevinson(a,efinal);
endfunction
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