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")
}
The input file "sinusoid.txt" is in the following link https://dpaste.de/M1VD
The input file data consists of two sine waves at frequencies of 50 and 120. The Matlab code produces the correct output given in the following link:
When the result from Matlab is scaled and the magnitude is taken, it correctly shows that the amplitude at a frequency of 50 is 0.7 and the amplitude at a frequency of 120 is 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)|')
The Swift code output is entirely different and unrecognizable when compared to the Matlab output, regardless of whatever scaling factors are applied and whether or not a real-to-complex or complex-to-complex transformation is applied:
Any ideas why this is?
The lengths of your 2 FFT are different, and so, of course the results won't match. You are also passing different amounts of data to your 2 FFTs.
Print out the FFT lengths and the input data vector to debug your code. Make sure the inputs match before comparing results.
Also, Apple's Accelerate/vDSP FFTs can use lengths other than just powers of 2 (lengths with factors of 3 or 5 are also allowed).
Also, note that Matlab indexes arrays starting at 1, not 0, as is more typical in C and Swift functions.