/
elimination_main.c
117 lines (99 loc) · 2.03 KB
/
elimination_main.c
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#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
void swap(double* a, double* b)
{
double c=*a;
*a=*b;
*b=c;
}
void swap_rows(double* m, int N, int r1, int r2)
{
for(int c=0; c<N; c++)
swap(m+r1*N+c, m+r2*N+c);
}
int find_pivot(double* m, int N, int r)
{
int p=r;
double val = fabs(m[r*N+r]);
for (int rp=r+1; rp<N; rp++)
if(fabs(m[rp*N+r])>val)
{
p=rp;
val = fabs(m[rp*N+r]);
}
return p;
}
void eliminate(double* m, int N, double* b)
{
for(int r=0; r<N-1; r++)
{
int p = find_pivot(m, N, r);
if(p != r)
{
swap_rows(m, N, r, p);
swap(b+r, b+p);
}
double piv = m[r*N+r];
// if(fabs(piv)<1e-20) {printf("matrix nearly singular ...."); abort();}
for(int rp = r+1; rp<N; rp++)
{
double fact = -m[rp*N+r]/piv;
for(int c=r; c<N; c++) m[rp*N+c]+=fact*m[r*N+c];
b[rp]+=fact*b[r];
}
}
}
void bks(double* m, int N, double* b, double* x)
{
for(int r=N-1; r>-1; --r)
{
double temp = b[r];
for (int c = r+1; c<N; ++c) temp -= m[r*N+c]*x[c];
x[r] = temp/m[r*N+r];
}
}
void solve_system (double* m, int N, double* b, double* x)
{
eliminate (m, N, b);
bks (m, N, b, x);
}
void print_matrix(double *p, int COLS,int ROWS)
{
for (int i=0;i<ROWS;i++)
{
for (int j=0;j<COLS;j++)
{
printf("%7.3f",p[i*COLS+j]);
}
puts(" ");
}
}
void init_matrix(double **p,int COLS,int ROWS)
{
*p = (double *)malloc(COLS*ROWS * sizeof(double));
for (int i=0;i<COLS*ROWS;i++)
{
(*p)[i] =(int)((double)rand()/RAND_MAX*10);
}
}
int main(int argc, char** argv)
{
int D=10;
srand(time(0));
double *A;
double *B;
init_matrix(&A,D,D);
init_matrix(&B,D,1);
printf("The first input matrix is:\n");
print_matrix(A,D,D);
printf("The Second input matrix is:\n");
print_matrix(B,D,1);
double *x = malloc(D*sizeof(double));
solve_system(A, D, B, x);
printf("The result is:\n");
print_matrix(x,D,1);
printf("\n");
return 0;
}