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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