import Cocoa
import Accelerate
let filePath = Bundle.main.path(forResource: "sinusoid", ofType: "txt")
let contentData = FileManager.default.contents(atPath: filePath!)
var content = NSString(data: contentData!, encoding: String.Encoding.utf8.rawValue) as? String
var idx = content?.characters.index(of: "\n")
idx = content?.index(after: idx!)
repeat {
//let fromIndex = index(from: )
content = content?.substring(from: idx!)
idx = content?.characters.index(of: "\n")
idx = content?.index(after: idx!)
} while content!.characters.contains("%")
let regex = try? NSRegularExpression(pattern: "[ ]+", options:[])
let delimiter = ","
var modifiedString = regex?.stringByReplacingMatches(in: content!, options: [], range: NSRange(location: 0, length: (content! as NSString).length), withTemplate: delimiter)
let lines = modifiedString?.components(separatedBy: "\n")
var s = [Double]()
for var line in lines! {
if !line.isEmpty {
let data = line.components(separatedBy: ",")
s.append(Double(data[1])!)
}
}
let length = vDSP_Length(pow(2, floor(log2(Float(s.count)))))
let L = Int(length)
// zrop or zop?
// zrop covers real to complex, and zop covers complex
// length must be a power of 2 or specific multiples of powers of 2 if size is at least 4
let setup = vDSP_DFT_zrop_CreateSetupD(nil, length, vDSP_DFT_Direction.FORWARD)
var inputReal = UnsafeMutablePointer<Double>.allocate(capacity: L)
var inputImaginary = UnsafeMutablePointer<Double>.allocate(capacity: L)
var outputReal = UnsafeMutablePointer<Double>.allocate(capacity: L)
var outputImaginary = UnsafeMutablePointer<Double>.allocate(capacity: L)
for i in 0..<L {
inputReal[i] = s[i]
inputImaginary[i] = 0.0
}
vDSP_DFT_ExecuteD(setup!, inputReal, inputImaginary, outputReal, outputImaginary)
for i in 0..<L {
print("\(outputReal[i]) + \(outputImaginary[i])i")
}
输入文件“sinusoid.txt”位于以下链接 https://dpaste.de/M1VD
输入文件数据由频率为 50 和 120 的两个正弦波组成。Matlab 代码生成以下链接中给出的正确输出:
当Matlab的结果被缩放并取大小时,它正确地表明频率为50的幅度为0.7,频率为120的幅度为1。
clear all; close all; clc;
data = load('sinusoid.txt');
S = data(:,2);
Fs = 1000;
Y = fft(S);
L = length(S);
P2 = abs(Y/L);
P1 = P2(1:L/2+1);
P1(2:end-1) = 2*P1(2:end-1);
f = Fs*(0:(L/2))/L;
plot(f,P1)
title('Single-Sided Amplitude Spectrum of X(t)')
xlabel('f (Hz)')
ylabel('|P1(f)|')
与 Matlab 输出相比,Swift 代码输出完全不同且无法识别,无论应用了何种比例因子以及是否应用了实数到复数或复数到复数的转换:
任何想法为什么会这样?