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hc2c

Convert a real-valued single-precision floating-point array in FFTPACK half-complex format to a single-precision complex floating-point array.

Installation

npm install @stdlib/fft-base-fftpack-float32-hc2c

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var hc2c = require( '@stdlib/fft-base-fftpack-float32-hc2c' );

hc2c( N, hc, strideHc, offsetHc, out, strideOut, offsetOut )

Converts a real-valued single-precision floating-point array in FFTPACK half-complex format to a single-precision complex floating-point array.

var Float32Array = require( '@stdlib/array-float32' );
var Complex64Array = require( '@stdlib/array-complex64' );
var floor = require( '@stdlib/math-base-special-floor' );
var rffti = require( '@stdlib/fft-base-fftpack-float32-rffti' );
var rfftf = require( '@stdlib/fft-base-fftpack-float32-rfftf' );

var N = 4;
var w = new Float32Array( ( 2*N ) + 34 );

rffti( N, w, 1, 0 );

var r = new Float32Array( [ 1.0, 2.0, 3.0, 4.0 ] );

rfftf( N, r, 1, 0, w, 1, 0 );
// r => <Float32Array>[ 10.0, -2.0, 2.0, -2.0 ]

var out = new Complex64Array( floor( N/2 ) + 1 );

hc2c( N, r, 1, 0, out, 1, 0 );
// out => <Complex64Array>[ 10.0, 0.0, -2.0, 2.0, -2.0, 0.0 ]

The function accepts the following arguments:

• N: length of the original real sequence.
• hc: input array in FFTPACK half-complex format.
• strideHc: stride length for hc.
• offsetHc: starting index for hc.
• out: output complex array.
• strideOut: stride length for out.
• offsetOut: starting index for out.

Notes

• FFTPACK's rfftf stores the forward DFT of a length N real sequence in N real values using the following layout:

  Even N: [ DC, Re(1), Im(1), Re(2), Im(2), ..., Re(N/2-1), Im(N/2-1), Nyquist ]
  Odd N:  [ DC, Re(1), Im(1), Re(2), Im(2), ..., Re((N-1)/2), Im((N-1)/2) ]
  

  where DC is the zero-frequency component and Nyquist is the component at frequency N/2 (even N only). Both are always purely real.

• The output is a complex-valued array of length floor(N/2) + 1. The DC and Nyquist components are stored with an explicit zero imaginary part.

• This half-complex format differs from other conventions (e.g., FFTW). In FFTW's half-complex format, all real components are stored first, followed by imaginary components in reverse order.

Examples

var Float32Array = require( '@stdlib/array-float32' );
var Complex64Array = require( '@stdlib/array-complex64' );
var floor = require( '@stdlib/math-base-special-floor' );
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var rffti = require( '@stdlib/fft-base-fftpack-float32-rffti' );
var rfftf = require( '@stdlib/fft-base-fftpack-float32-rfftf' );
var hc2c = require( '@stdlib/fft-base-fftpack-float32-hc2c' );

var N = 8;
var opts = {
    'dtype': 'float32'
};
var r = discreteUniform( N, -10, 10, opts );
var w = new Float32Array( ( 2*N ) + 34 );

console.log( r );

rffti( N, w, 1, 0 );
rfftf( N, r, 1, 0, w, 1, 0 );

console.log( r );

var out = new Complex64Array( floor( N/2 ) + 1 );

hc2c( N, r, 1, 0, out, 1, 0 );

console.log( out );

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.