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functions in fitrat.i  f
fitpol

yp= fitpol(y, x, xp)
or yp= fitpol(y, x, xp, keep=1)
is an interpolation routine similar to interp, except that fitpol
returns the polynomial of degree numberof(X)1 which passes through
the given points (X,Y), evaluated at the requested points XP.
The X must either increase or decrease monotonically.
If the KEEP keyword is present and nonzero, the external variable
yperr will contain a list of error estimates for the returned values
yp on exit.
The algorithm is taken from Numerical Recipes (Press, et. al.,
Cambridge University Press, 1988); it is called Neville's algorithm.
The rational function interpolator fitrat is better for "typical"
functions. The Yorick implementaion requires numberof(X)*numberof(XP)
temporary arrays, so the X and Y arrays should be reasonably small.
interpreted function, defined at i/fitrat.i line 10

SEE ALSO:

fitrat,
interp

fitrat

yp= fitrat(y, x, xp)
or yp= fitrat(y, x, xp, keep=1)
is an interpolation routine similar to interp, except that fitpol
returns the diagonal rational function of degree numberof(X)1 which
passes through the given points (X,Y), evaluated at the requested
points XP. (The numerator and denominator polynomials have equal
degree, or the denominator has one larger degree.)
The X must either increase or decrease monotonically. Also, this
algorithm works by recursion, fitting successively to consecutive
pairs of points, then consecutive triples, and so forth.
If there is a pole in any of these fits to subsets, the algorithm
fails even though the rational function for the final fit is non
singular. In particular, if any of the Y values is zero, the
algorithm fails, and you should be very wary of lists for which
Y changes sign. Note that if numberof(X) is even, the rational
function is Ytranslation invariant, while numberof(X) odd generally
results in a nontranslatable fit (because it decays to y=0).
If the KEEP keyword is present and nonzero, the external variable
yperr will contain a list of error estimates for the returned values
yp on exit.
The algorithm is taken from Numerical Recipes (Press, et. al.,
Cambridge University Press, 1988); it is called the BulirschStoer
algorithm. The Yorick implementaion requires numberof(X)*numberof(XP)
temporary arrays, so the X and Y arrays should be reasonably small.
interpreted function, defined at i/fitrat.i line 72

SEE ALSO:

fitpol,
interp

