php 时频分析函数（时频分析方法）

在PHP中，可以使用FFT（快速傅里叶变换）算法来进行时频分析。以下是一个使用PHP实现FFT算法的示例代码：

function fft($data) {
    $n = count($data);

    if ($n == 1) {
        return $data;
    }

    $even = [];
    $odd = [];

    for ($i = 0; $i < $n; $i++) {
        if ($i % 2 == 0) {
            $even[] = $data[$i];
        } else {
            $odd[] = $data[$i];
        }
    }

    $evenResult = fft($even);
    $oddResult = fft($odd);

    $result = [];

    for ($k = 0; $k < $n / 2; $k++) {
        $angle = -2 * pi() * $k / $n;
        $twiddle = complexExp($angle);

        $temp = $twiddle * $oddResult[$k];

        $result[$k] = $evenResult[$k] + $temp;
        $result[$k + $n / 2] = $evenResult[$k] - $temp;
    }

    return $result;
}

function complexExp($angle) {
    $real = cos($angle);
    $imaginary = sin($angle);

    return new Complex($real, $imaginary);
}

class Complex {
    public $real;
    public $imaginary;

    public function __construct($real, $imaginary) {
        $this->real = $real;
        $this->imaginary = $imaginary;
    }

    public function __mul($other) {
        $real = $this->real * $other->real - $this->imaginary * $other->imaginary;
        $imaginary = $this->real * $other->imaginary + $this->imaginary * $other->real;

        return new Complex($real, $imaginary);
    }

    public function __add($other) {
        $real = $this->real + $other->real;
        $imaginary = $this->imaginary + $other->imaginary;

        return new Complex($real, $imaginary);
    }
}

使用示例：

$data = [1, 2, 3, 4, 5, 6, 7, 8];
$result = fft($data);

foreach ($result as $complex) {
    echo sqrt($complex->real * $complex->real + $complex->imaginary * $complex->imaginary) . "\n";
}

上述代码实现了一个简单的FFT算法，并对输入数据进行了时频分析。你可以根据自己的需求对其进行修改和扩展。