Algorithms Index


AutoPad

Author : Ian Taylor, Bernard Schutz
Date : 30 August 2000
Version: 2.01
 


Autopad extends the input data set (of type VectorType) with zeros to make the total number of data items equal to the nearest larger power of two. Autopad has no parameters in order to make it convenient to use with the FFT unit in order to make the FFT run most efficiently. If the input set is already a power of 2 it is not extended.

The way that this unit acts on VectorType inputs varies according to the type. A pure VectorType will be extended as described above.  If the data are irregularly sampled, they will be extended with a regular spacing equal to the size of the first or last data interval, according to whether they are placed at the beginning or the end. A SampleSet or a ComplexSampleSet will be extended as described above and its sampling rate will not be changed. A Spectrum or ComplexSpectrum will be extended as described above; its frequency resolution will not be changed, and the parameter nFull (the number of points in the full data set from which it might have been derived by a Fourier transform) is increased to the new size.  If the spectral data are narrow-band, the new length of the extended set is interpreted as the size of nFull, not the size of the bandwidth of the data held in the object. Note that Spectrum and ComplexSpectrum data sets cannot be extended at the front, since it does not make sense to add points below zero frequency. More details are given in the documentation for these spectral types. If the input set is a Histogram, then the data set will be extended as described above. If the zeros are to be added at the beginning and the first delimiter is negative infinity, then nothing is done; similarly if the zeros are to be added at the end and the last delimiter is positive infinity, nothing is done.