source code
/* The Computer Language Benchmarks Game
* https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
*
* Contributed by Mr Ledrug
*
* Algorithm lifted from Intel Fortran #2 code by Steve Decker et al.
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
inline int A(int i, int j) {
return ((i+j) * (i+j+1) / 2 + i + 1);
}
double dot(double * v, double * u, int n) {
int i;
double sum = 0;
for (i = 0; i < n; i++)
sum += v[i] * u[i];
return sum;
}
void mult_Av(double * v, double * out, const int n) {
int i, j;
double sum;
# pragma omp parallel for private(sum,j)
for (i = 0; i < n; i++) {
for (sum = j = 0; j < n; j++)
sum += v[j] / A(i,j);
out[i] = sum;
}
}
void mult_Atv(double * v, double * out, const int n) {
int i, j;
double sum;
# pragma omp parallel for private(sum,j)
for (i = 0; i < n; i++) {
for (sum = j = 0; j < n; j++)
sum += v[j] / A(j,i);
out[i] = sum;
}
}
double *tmp;
void mult_AtAv(double *v, double *out, const int n) {
mult_Av(v, tmp, n);
mult_Atv(tmp, out, n);
}
int main(int argc, char**argv) {
int n = atoi(argv[1]);
if (n <= 0) n = 2000;
double *u, *v;
u = malloc(n * sizeof(double));
v = malloc(n * sizeof(double));
tmp = malloc(n * sizeof(double));
int i;
for (i = 0; i < n; i++) u[i] = 1;
for (i = 0; i < 10; i++) {
mult_AtAv(u, v, n);
mult_AtAv(v, u, n);
}
printf("%.9f\n", sqrt(dot(u,v, n) / dot(v,v,n)));
return 0;
}
notes, command-line, and program output
NOTES:
64-bit Ubuntu quad core
13.2.0-23ubuntu4
Mon, 03 Jun 2024 22:48:45 GMT
MAKE:
/usr/bin/gcc -pipe -Wall -O3 -fomit-frame-pointer -march=ivybridge -fopenmp spectralnorm.gcc-3.c -o spectralnorm.gcc-3.gcc_run -lm
rm spectralnorm.gcc-3.c
2.80s to complete and log all make actions
COMMAND LINE:
./spectralnorm.gcc-3.gcc_run 5500
PROGRAM OUTPUT:
1.274224153