Convert prediction filter polynomial to reflection coefficients

`k`

` = `

poly2rc(a)

[k,r0]` = `

poly2rc(a,efinal)

`k`

converts
the prediction filter polynomial ` = `

poly2rc(a)`a`

to the reflection
coefficients of the corresponding lattice structure. `a`

can
be real or complex, and `a(1)`

cannot be 0. If `a(1)`

is
not equal to `1`

, poly2rc normalizes
the prediction filter polynomial by `a(1)`

. `k`

is
a row vector of size `length(a)-1`

.

`[k,r0]`

returns the zero-lag
autocorrelation, ` = `

poly2rc(a,efinal)`r0`

, based on the final prediction
error, `efinal`

.

If `abs(k(i)) == 1`

for any `i`

,
finding the reflection coefficients is an ill-conditioned problem. `poly2rc`

returns
some `NaN`

s and provides a warning message in those
cases.

[1] Kay, Steven M. *Modern Spectral
Estimation*. Englewood Cliffs, NJ: Prentice-Hall, 1988.

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