diff --git a/numerical_methods/fast_fourier_transform.cpp b/numerical_methods/fast_fourier_transform.cpp index 9e56849e9..725120c15 100644 --- a/numerical_methods/fast_fourier_transform.cpp +++ b/numerical_methods/fast_fourier_transform.cpp @@ -1,70 +1,75 @@ /** * @file - * @brief [A fast Fourier transform (FFT)](https://medium.com/@aiswaryamathur/understanding-fast-fouriertransform-from-scratch-to-solve-polynomial-multiplication-8018d511162f) is an algorithm that computes the - * discrete Fourier transform (DFT) of a sequence , or its inverse (IDFT) , this algorithm - * has application in use case scenario where a user wants to find points of a function - * in short period time by just using the coefficents of the polynomial function. + * @brief [A fast Fourier transform + (FFT)](https://medium.com/@aiswaryamathur/understanding-fast-fouriertransform-from-scratch-to-solve-polynomial-multiplication-8018d511162f) + is an algorithm that computes the + * discrete Fourier transform (DFT) of a sequence , or its inverse (IDFT) , this + algorithm + * has application in use case scenario where a user wants to find points of a + function + * in short period time by just using the coefficents of the polynomial + function. * @details * https://medium.com/@aiswaryamathur/understanding-fast-fourier-transform-from-scratch-to -solve-polynomial-multiplication-8018d511162f * @author [Ameya Chawla](https://github.com/ameyachawlaggsipu) */ -#include /// for IO operations -#include /// for mathematical-related functions -#include /// for storing points and coefficents -#include /// for assert -#include /// for storing test cases +#include /// for assert +#include /// for mathematical-related functions +#include /// for storing points and coefficents +#include /// for IO operations +#include /// for storing test cases /** - * @brief FastFourierTransform is a recursive function which returns list of complex numbers + * @brief FastFourierTransform is a recursive function which returns list of + * complex numbers * @param p List of Coefficents in form of complex numbers * @param n Count of elements in list p * @returns p if n==1 * @returns y if n!=1 */ -std::complex* FastFourierTransform(std::complex*p ,uint64_t n) -{ - double pi = 2*asin(1.0);///Declaring value of pi - - if(n==1) return p; ///Base Case To return +std::complex *FastFourierTransform(std::complex *p, + uint64_t n) { + double pi = 2 * asin(1.0); /// Declaring value of pi - std::complex om=std::complex(cos(2*pi/n),sin(2*pi/n)); ///Calculating value of omega + if (n == 1) + return p; /// Base Case To return - std::complex *pe= new std::complex[n/2]; /// Coefficents of even power + std::complex om = std::complex( + cos(2 * pi / n), sin(2 * pi / n)); /// Calculating value of omega - std::complex *po= new std::complex[n/2]; ///Coefficents of odd power + auto *pe = new std::complex[n / 2]; /// Coefficents of even power - uint64_t k1=0,k2=0; - for(uint64_t j=0;j[n / 2]; /// Coefficents of odd power - } - else po[k2++]=p[j]; ///Assigning value of odd coefficents + uint64_t k1 = 0, k2 = 0; + for (uint64_t j = 0; j < n; j++) { + if (j % 2 == 0) { + pe[k1++] = p[j]; /// Assigning values of even coefficents + } else + po[k2++] = p[j]; /// Assigning value of odd coefficents + } - } + std::complex *ye = + FastFourierTransform(pe, n / 2); /// Recursive Call - std::complex*ye=FastFourierTransform(pe,n/2);///Recursive Call - - std::complex*yo=FastFourierTransform(po,n/2);///Recursive Call + std::complex *yo = + FastFourierTransform(po, n / 2); /// Recursive Call - std::complex*y=new std::complex[n];///Final value representation list + auto *y = new std::complex[n]; /// Final value representation list - - for(uint64_t i=0;i* FastFourierTransform(std::complex*p ,uint64_t n) */ static void test() { /* descriptions of the following test */ - - std::complex *t1= new std::complex[2];///Test case 1 - t1[0]={1,0}; - t1[1]={2,0}; - - std::complex *t2=new std::complex[4];///Test case 2 - t2[0]={1,0}; - t2[1]={2,0}; - t2[2]={3,0}; - t2[3]={4,0}; - + auto *t1 = new std::complex[2]; /// Test case 1 + t1[0] = {1, 0}; + t1[1] = {2, 0}; - uint8_t n1=sizeof(t1)/sizeof(std::complex); - uint8_t n2=sizeof(t2)/sizeof(std::complex); + auto *t2 = new std::complex[4]; /// Test case 2 + t2[0] = {1, 0}; + t2[1] = {2, 0}; + t2[2] = {3, 0}; + t2[3] = {4, 0}; - - std::vector> r1={{3,0},{-1,0} };///True Answer for test case 1 - - std::vector> r2={{10,0},{-2,-2},{-2,0},{-2,2} };///True Answer for test case 2 - + uint8_t n1 = sizeof(t1) / sizeof(std::complex); + uint8_t n2 = sizeof(t2) / sizeof(std::complex); - std::complex *o1=FastFourierTransform(t1,n1); - std::complex *o2=FastFourierTransform(t2,n2); - - - for(uint8_t i=0;ireal()<0.000000000001 ) && (r1[i].imag()-o1->imag()<0.000000000001 ));/// Comparing for both real and imaginary values for test case 1 + std::vector> r1 = { + {3, 0}, {-1, 0}}; /// True Answer for test case 1 + + std::vector> r2 = { + {10, 0}, {-2, -2}, {-2, 0}, {-2, 2}}; /// True Answer for test case 2 + + std::complex *o1 = FastFourierTransform(t1, n1); + std::complex *o2 = FastFourierTransform(t2, n2); + + for (uint8_t i = 0; i < n1; i++) { + assert((r1[i].real() - o1->real() < 0.000000000001) && + (r1[i].imag() - o1->imag() < + 0.000000000001)); /// Comparing for both real and imaginary + /// values for test case 1 o1++; } - - for(uint8_t i=0;ireal()<0.000000000001 ) && ( r2[i].imag()-o2->imag()<0.000000000001 ));/// Comparing for both real and imaginary values for test case 2 + + for (uint8_t i = 0; i < n2; i++) { + assert((r2[i].real() - o2->real() < 0.000000000001) && + (r2[i].imag() - o2->imag() < + 0.000000000001)); /// Comparing for both real and imaginary + /// values for test case 2 o2++; } - + delete[] o1; delete[] o2; delete[] t1; delete[] t2; - } /** @@ -127,8 +132,7 @@ static void test() { * calls automated test function to test the working of fast fourier transform. * @returns 0 on exit */ -int main(int argc, char const *argv[]) -{ - test(); // run self-test implementations - return 0; +int main(int argc, char const *argv[]) { + test(); // run self-test implementations + return 0; }