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晚上好!我正在尝试使用在 Android 中的 Java 中工作的 FFT 代码,但不知道为什么它不能正常工作。这是我在 Android 中修改后的代码。提前致谢!!

package dani;

public class FFT {



    // compute the FFT of x[], assuming its length is a power of 2
    public static Complex[] fft(Complex[] x) {
        int N = x.length;

        // base case
        if (N == 1) return new Complex[] { x[0] };

        // radix 2 Cooley-Tukey FFT
        if (N % 2 != 0) { throw new RuntimeException("N is not a power of 2"); }

        // fft of even terms
        Complex[] even = new Complex[N/2];
        for (int k = 0; k < N/2; k++) {
            even[k] = x[2*k];
        }
        Complex[] q = fft(even);

        // fft of odd terms
        Complex[] odd  = even;  // reuse the array
        for (int k = 0; k < N/2; k++) {
            odd[k] = x[2*k + 1];
        }
        Complex[] r = fft(odd);

        // combine
        Complex[] y = new Complex[N];
        for (int k = 0; k < N/2; k++) {
            double kth = -2 * k * Math.PI / N;
            Complex wk = new Complex(Math.cos(kth), Math.sin(kth));
            y[k]       = q[k].plus(wk.times(r[k]));
            y[k + N/2] = q[k].minus(wk.times(r[k]));
        }
        return y;
    }


    // compute the inverse FFT of x[], assuming its length is a power of 2
    public static Complex[] ifft(Complex[] x) {
        int N = x.length;
        Complex[] y = new Complex[N];

        // take conjugate
        for (int i = 0; i < N; i++) {
            y[i] = x[i].conjugate();
        }

        // compute forward FFT
        y = fft(y);

        // take conjugate again
        for (int i = 0; i < N; i++) {
            y[i] = y[i].conjugate();
        }

        // divide by N
        for (int i = 0; i < N; i++) {
            y[i] = y[i].times(1.0 / N);
        }

        return y;

    }

    // compute the circular convolution of x and y
    public static Complex[] cconvolve(Complex[] x, Complex[] y) {

        // should probably pad x and y with 0s so that they have same length
        // and are powers of 2
        if (x.length != y.length) { throw new RuntimeException("Dimensions don't  
 agree"); }

        int N = x.length;

        // compute FFT of each sequence
        Complex[] a = fft(x);
        Complex[] b = fft(y);

        // point-wise multiply
        Complex[] c = new Complex[N];
        for (int i = 0; i < N; i++) {
            c[i] = a[i].times(b[i]);
        }

        // compute inverse FFT
        return ifft(c);
    }


    // compute the linear convolution of x and y
    public static Complex[] convolve(Complex[] x, Complex[] y) {
        Complex ZERO = new Complex(0, 0);

        Complex[] a = new Complex[2*x.length];
        for (int i = 0;        i <   x.length; i++) a[i] = x[i];
        for (int i = x.length; i < 2*x.length; i++) a[i] = ZERO;

        Complex[] b = new Complex[2*y.length];
        for (int i = 0;        i <   y.length; i++) b[i] = y[i];
        for (int i = y.length; i < 2*y.length; i++) b[i] = ZERO;

        return cconvolve(a, b);
    }



    }



    public static void main(String[] args) { 
        int N = 64;
        Complex[] x = new Complex[N];

        // original data
        for (int i = 0; i < N; i++) {
            x[i] = new Complex(i, 0);
            x[i] = new Complex(-2*Math.cos(i)/N, 0);//AQUI se mete la funcion
        }


        // FFT of original data
        Complex[] y = fft(x);


        // take inverse FFT
        Complex[] z = ifft(y);


        // circular convolution of x with itself
        Complex[] c = cconvolve(x, x);


        // linear convolution of x with itself
        Complex[] d = convolve(x, x);

    }

}

我已经为复数定义了另一个类,这是代码:

package dani;



public class Complex {
private final double re;   // the real part
private final double im;   // the imaginary part

// create a new object with the given real and imaginary parts
public Complex(double real, double imag) {
    re = real;
    im = imag;
}

// return a string representation of the invoking Complex object
public String toString() {
    if (im == 0) return re + "";
    if (re == 0) return im + "i";
    if (im <  0) return re + " - " + (-im) + "i";
    return re + " + " + im + "i";
}

// return abs/modulus/magnitude and angle/phase/argument
public double abs()   { return Math.hypot(re, im); }  // Math.sqrt(re*re + im*im)
public double phase() { return Math.atan2(im, re); }  // between -pi and pi

// return a new Complex object whose value is (this + b)
public Complex plus(Complex b) {
    Complex a = this;             // invoking object
    double real = a.re + b.re;
    double imag = a.im + b.im;
    return new Complex(real, imag);
}

// return a new Complex object whose value is (this - b)
public Complex minus(Complex b) {
    Complex a = this;
    double real = a.re - b.re;
    double imag = a.im - b.im;
    return new Complex(real, imag);
}

// return a new Complex object whose value is (this * b)
public Complex times(Complex b) {
    Complex a = this;
    double real = a.re * b.re - a.im * b.im;
    double imag = a.re * b.im + a.im * b.re;
    return new Complex(real, imag);
}

// scalar multiplication
// return a new object whose value is (this * alpha)
public Complex times(double alpha) {
    return new Complex(alpha * re, alpha * im);
}

// return a new Complex object whose value is the conjugate of this
public Complex conjugate() {  return new Complex(re, -im); }

// return a new Complex object whose value is the reciprocal of this
public Complex reciprocal() {
    double scale = re*re + im*im;
    return new Complex(re / scale, -im / scale);
}

// return the real or imaginary part
public double re() { return re; }
public double im() { return im; }

// return a / b
public Complex divides(Complex b) {
    Complex a = this;
    return a.times(b.reciprocal());
}

// return a new Complex object whose value is the complex exponential of this
public Complex exp() {
    return new Complex(Math.exp(re) * Math.cos(im), Math.exp(re) * Math.sin(im));
}

// return a new Complex object whose value is the complex sine of this
public Complex sin() {
    return new Complex(Math.sin(re) * Math.cosh(im), Math.cos(re) * Math.sinh(im));
}

// return a new Complex object whose value is the complex cosine of this
public Complex cos() {
    return new Complex(Math.cos(re) * Math.cosh(im), -Math.sin(re) * Math.sinh(im));
}

// return a new Complex object whose value is the complex tangent of this
public Complex tan() {
    return sin().divides(cos());
}



// a static version of plus
public static Complex plus(Complex a, Complex b) {
    double real = a.re + b.re;
    double imag = a.im + b.im;
    Complex sum = new Complex(real, imag);
    return sum;
}






}
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