Package org.hipparchus.transform

Class FastFourierTransformer

java.lang.Object
org.hipparchus.transform.FastFourierTransformer
All Implemented Interfaces:
Serializable
public class FastFourierTransformer extends Object implements Serializable
Implements the Fast Fourier Transform for transformation of one-dimensional real or complex data sets. For reference, see Applied Numerical Linear Algebra, ISBN 0898713897, chapter 6.

There are several variants of the discrete Fourier transform, with various normalization conventions, which are specified by the parameter DftNormalization.

The current implementation of the discrete Fourier transform as a fast Fourier transform requires the length of the data set to be a power of 2. This greatly simplifies and speeds up the code. Users can pad the data with zeros to meet this requirement. There are other flavors of FFT, for reference, see S. Winograd, On computing the discrete Fourier transform, Mathematics of Computation, 32 (1978), 175 - 199.

See Also:

  • Constructor Details

    • FastFourierTransformer

      public FastFourierTransformer(DftNormalization normalization)
      Creates a new instance of this class, with various normalization conventions.
      Parameters:
      normalization - the type of normalization to be applied to the transformed data

  • Method Details

    • transformInPlace

      public static void transformInPlace(double[][] dataRI, DftNormalization normalization, TransformType type)
      Computes the standard transform of the specified complex data. The computation is done in place. The input data is laid out as follows
      • dataRI[0][i] is the real part of the i-th data point,
      • dataRI[1][i] is the imaginary part of the i-th data point.
      Parameters:
      dataRI - the two dimensional array of real and imaginary parts of the data
      normalization - the normalization to be applied to the transformed data
      type - the type of transform (forward, inverse) to be performed
      Throws:
      MathIllegalArgumentException - if the number of rows of the specified array is not two, or the array is not rectangular
      MathIllegalArgumentException - if the number of data points is not a power of two

    • transform

      public Complex[] transform(double[] f, TransformType type)
      Returns the (forward, inverse) transform of the specified real data set.
      Parameters:
      f - the real data array to be transformed
      type - the type of transform (forward, inverse) to be performed
      Returns:
      the complex transformed array
      Throws:
      MathIllegalArgumentException - if the length of the data array is not a power of two

    • transform

      public Complex[] transform(UnivariateFunction f, double min, double max, int n, TransformType type)
      Returns the (forward, inverse) transform of the specified real function, sampled on the specified interval.
      Parameters:
      f - the function to be sampled and transformed
      min - the (inclusive) lower bound for the interval
      max - the (exclusive) upper bound for the interval
      n - the number of sample points
      type - the type of transform (forward, inverse) to be performed
      Returns:
      the complex transformed array
      Throws:
      MathIllegalArgumentException - if the lower bound is greater than, or equal to the upper bound
      MathIllegalArgumentException - if the number of sample points n is negative
      MathIllegalArgumentException - if the number of sample points n is not a power of two

    • transform

      public Complex[] transform(Complex[] f, TransformType type)
      Returns the (forward, inverse) transform of the specified complex data set.
      Parameters:
      f - the complex data array to be transformed
      type - the type of transform (forward, inverse) to be performed
      Returns:
      the complex transformed array
      Throws:
      MathIllegalArgumentException - if the length of the data array is not a power of two