| Non-monotonic Abscissa values for IDL function SPLINE_P [message #66716] |
Tue, 02 June 2009 09:40 |
Xavier Ceamanos Garci
Messages: 2
Registered: June 2009
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Junior Member |
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Hi folks!
I have a question regarding the IDL SPLINE_P function. It works as
follows...
SPLINE_P, X, Y, Xr, Yr, [INTERVAL]
Where 'X' is the original abscissa vector (let's say 0:1:249, in my
example) and 'Y' the vector I'd like to interpolate (n_elements(Y)
=250, of course).
Then 'Xr' and 'Yr' are the outputs containing the abscissa values of
the interpolated function and the interpolated vector, respectively.
The keyword INTERVAL sets the desired interval between interpolants.
The problem appears when checking the output Xr and Yr size. Normally,
their size should be (250-1)*INTERVAL+1. However, that is not the
case. For INTERVAL=100 I get an output size equal to 25147 instead of
24901. The reason is that the output abscissa is not monotonic and
that does allow me to continue working with the Y output.
Does anyone know how to make it monotonic?
I would like to use this function instead of SPLINE since the latter
is bloody slower than the the first!
I thank you all in advance,
Cheers,
Xavi
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