/* 
 * Discrete Fourier transform (Java)
 * by Project Nayuki, 2017. Public domain.
 * https://www.nayuki.io/page/how-to-implement-the-discrete-fourier-transform
 */


public final class Dft {
	
	/* 
	 * Computes the discrete Fourier transform (DFT) of the given complex vector.
	 * All the array arguments must be non-null and have the same length.
	 */
	public static void computeDft(double[] inreal, double[] inimag, double[] outreal, double[] outimag) {
		int n = inreal.length;
		for (int k = 0; k < n; k++) {  // For each output element
			double sumreal = 0;
			double sumimag = 0;
			for (int t = 0; t < n; t++) {  // For each input element
				double angle = 2 * Math.PI * t * k / n;
				sumreal +=  inreal[t] * Math.cos(angle) + inimag[t] * Math.sin(angle);
				sumimag += -inreal[t] * Math.sin(angle) + inimag[t] * Math.cos(angle);
			}
			outreal[k] = sumreal;
			outimag[k] = sumimag;
		}
	}
	
}