Displaying 3 results from an estimated 3 matches for "phi_3".
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2005 Jun 01
2
Fitting ARMA model with known inputs.
Hello!
Is it possible to use R time series to identificate a process which is
subjected to known input? I.e. I have 2 sequences - one is measurements
of black box's state and the second is the "force" by which this black
box is driven (which is known too) and I want to fit thist two series
with AR-process. The "ar" procedure from stats package expects that the
force is
2007 Apr 10
1
Testing invertibility of an AR model
...an't find the method in R for testing whether
the resulting estimated coefficients
of an AR model imply that the model is invertible.
To quote from eric zivot's blue book :
" the AR(p) is invertible provided the rots of the characteristic
equation
Phi(z) = 1 - phi_1*z - phi_2*z^2 = phi_3*z^3 - ..... Phi_p*z^p = 0 lie
outside
the complex circle".
I can't find a function nor do I know how to do the above myself. I
think there is an equivalent method in which
I can check whether the eigenvalues of some dual equation ( I forget
what it is ) are less than one but I don't...
2006 Aug 16
0
confusing about contrasts concept [long]
...1/12 1/4
(ginverse() will be available in S+4.0 and fractions(), now available in
the MASS2 library, simply displays numbers in fractional form so that
patterns are more obvious).
Thus the phi's are identified by requiring that they add to zero, and
*alpha_l = (phi_2 - phi_l )/2,
*alpha_2 = [phi_3 - (phi_l + phi_2)/2] / 3
&c. When the columns of C are not mutually orthogonal the story is not
quite so obvious, though. For example take a C matrix using contr.sdif
(available in the MASS2 library)
> contr.sdif(4)
[2-1] [3-2] [4-3]
1 -0.75 -0.5 -0.25
2 0.25 -0.5 -0.25
3 0.25 0.5 -0.25
4...