From 143f81381ace033913393ac7f45ee4f329b8316f Mon Sep 17 00:00:00 2001
From: Esteban Medero <estebanmedero@Estebans-MBP.attlocal.net>
Date: Sun, 1 Oct 2023 20:02:43 -0400
Subject: [PATCH] implementation of simple DFT algorithm

---
 DFTAlgorithm/dft.h    | 66 +++++++++++++++++++++++++++++++++++++++++++
 DFTAlgorithm/main.cpp | 39 +++++++++++++++++++++++++
 2 files changed, 105 insertions(+)
 create mode 100644 DFTAlgorithm/dft.h
 create mode 100644 DFTAlgorithm/main.cpp

diff --git a/DFTAlgorithm/dft.h b/DFTAlgorithm/dft.h
new file mode 100644
index 0000000..c012954
--- /dev/null
+++ b/DFTAlgorithm/dft.h
@@ -0,0 +1,66 @@
+/*
+This is an algorithm for the implementation of the Discrete Fourier Transform
+or DFT. It is widely used in many signal and data processing applications and is mathematically
+defined as a change of basis from the time domain to the frequency domain. It was first implemented
+simply, as the Fourier Transform, by Joseph Fourier during his studies of the heat equation. 
+This was made on the observation that an oscillatory measurement can be defined as a linear
+combinations of simple sinusoids at different frequencies. Below is the implementation for the 
+DFT:
+
+The DFT is defined as the inner product of a signal to the complex plane C of intervals proportional to the
+number of samples taken in the signal.
+
+given a signal x(n) we can convert to the frequency X(k)
+
+X(k) = SUM(x(n) * e^(i*theta)) with theta = (-j * 2pi * k * n) / N 
+on the interval n = 0 to n = N - 1 for every value of k = 0 to k = N - 1
+
+*/
+#ifndef DFT_H
+#define DFT_H
+
+#include <iostream>
+#include <cmath>
+#include <vector>
+
+using namespace std;
+
+//Since the we know e^i * theta can be represented as euler's equation:
+// e ^ i * theta = cos(theta) + i * sin(theta)
+//The DFT must return two valued pairs as coordinates on the unit circle
+//With the cos representing the Re or horizontal axis and sin representing
+//the imaginary or veritcal axis
+vector<pair<float,float>> DFT(vector<float> timeDomain)
+{
+    vector<pair<float, float>> frequencyDomain;
+
+    //holds the position of the current DFT coefficient
+    for(int i = 0; i < timeDomain.size(); i++)
+    {
+
+        //initialize two values to store the real and imaginary portion of
+        //DFT coefficient
+        float DFT_real = 0.0f;
+        float DFT_imaginary = 0.0f;
+
+        //Iterates over each value in the time domain signal 
+        //and takes the sum of the products of the time domain value with
+        //the complex exponential
+        for(int j = 0; j < timeDomain.size(); j++)
+        {
+            //each value of splits the real and imaginary part
+            DFT_real += timeDomain.at(j) * (cos((2*M_PI*i*j)/timeDomain.size()));
+            DFT_imaginary += -1 * timeDomain.at(j) * sin((2*M_PI*i*j)/timeDomain.size());
+        }
+
+        //push next DFT coefficient to the vector
+        frequencyDomain.push_back(make_pair(DFT_real, DFT_imaginary));
+    }
+
+    //return frequency representation of a signal
+    return frequencyDomain;
+
+}
+
+#endif
+
diff --git a/DFTAlgorithm/main.cpp b/DFTAlgorithm/main.cpp
new file mode 100644
index 0000000..e0bc49b
--- /dev/null
+++ b/DFTAlgorithm/main.cpp
@@ -0,0 +1,39 @@
+#include<iostream>
+#include "dft.h"
+
+int main()
+{
+    vector<float> timeDomain;
+    vector<pair<float, float>> frequencyDomain;
+
+    //Here we define a simple function to implement 
+    //This can be visualized as a sawtooth wave form
+    //if you want to extend the length to represent 
+    //a much more realistic sampling margin you can extend with Karplus-Strong Algorithm
+    //stay tuned for this implementation
+    for(float i = 0; i < 1.02; i += 0.02)
+    {
+        timeDomain.push_back(i - 0.5);
+    }
+
+    //Here we call the DFT implementation can be found in dft.h
+    frequencyDomain = DFT(timeDomain);
+    
+    //print time domain coefficients
+    for(int i = 0; i < timeDomain.size(); i++)
+    {
+        cout << timeDomain.at(i) << " ";
+    }
+
+    //place space between the output
+    cout << endl;
+
+    //print out absolute value or magnitude of complex DFT coefficients
+    //here |a + bi| = sqrt(a^2 + b^2)
+    for(int i = 0; i < timeDomain.size(); i++)
+    {
+        cout << sqrt(pow(frequencyDomain.at(i).first, 2) + pow(frequencyDomain.at(i).second, 2)) << " ";
+    }
+   
+    return 0;
+}
\ No newline at end of file