// TODO implement error handling
void row_echolon_form(index_type start) {
if (start == std::min(rows, cols)) return;
index_type not_found = n_pos;
// sort the rows so that the row with the first leading
// pivot element is the top row
std::sort(data.begin(), data.end(),
[not_found](const std::array<double, m> &row_one,
const std::array<double, m> &row_two){
return find_pivot(row_one, not_found) < find_pivot(row_two, not_found);
});
// get pivot for first row
index_type pivot = find_pivot(start);
for (index_type i = start + 1; i < rows; i++) {
index_type curr_pivot = find_pivot(i);
// if there's no pivot element in this row then there will be no
// pivot element in this column in some row later on, because the rows
// have been sorted by the position of the row's pivot element.
if (curr_pivot != pivot)
break;
// pivot * x = -curr_pivot; | / pivot
// x = - curr_pivot / pivot;
scale_and_add(start, i, -(data[i][curr_pivot] / data[start][pivot]));
}
row_echolon_form(start + 1);
}
int QUERN_solve_with_CGNR(int m,
int n,
const int* A_row_start,
const int* A_column_index,
const double* A_value,
const double* rhs,
const int* R_row_start,
const int* R_column_index,
const double* R_value,
int max_iterations,
double absolute_convergence_tolerance,
double* x,
int* return_solved,
int* return_iterations,
double* return_residual_norm)
{
if(m<=0 || n<=0 || !A_row_start || !A_column_index || !A_value
|| !rhs || !R_row_start || !R_column_index || !R_value || !x
|| !return_solved || !return_iterations || !return_residual_norm)
return QUERN_INPUT_ERROR;
// default values
*return_solved=0;
*return_iterations=0;
*return_residual_norm=two_norm(n, rhs);
if(*return_residual_norm<=absolute_convergence_tolerance){
*return_solved=1;
return QUERN_OK;
}
// allocate some room to work in
double* working_vectors=(double*)std::malloc((3*n+m)*sizeof(double));
if(!working_vectors)
return QUERN_OUT_OF_MEMORY;
double* r=working_vectors;
double* s=r+n;
double* z=s+n;
double* u=z+n;
// set up CGNR
int check;
std::memset(x, 0, n*sizeof(double));
std::memcpy(r, rhs, n*sizeof(double));
std::memcpy(u, rhs, n*sizeof(double));
check=QUERN_solve_with_r_transpose_in_place(n, R_row_start, R_column_index,
R_value, u);
if(check){ std::free(working_vectors); return check; }
check=QUERN_solve_with_r(n, R_row_start, R_column_index, R_value, u, z);
if(check){ std::free(working_vectors); return check; }
std::memcpy(s, z, n*sizeof(double));
double rho=two_norm_squared(n, u);
// the main loop
for(;;){
if(rho==0){ std::free(working_vectors); return QUERN_INPUT_ERROR; }
check=QUERN_multiply(m, n, A_row_start, A_column_index, A_value, s, u);
if(check){ std::free(working_vectors); return check; }
check=QUERN_multiply_transpose(m, n, A_row_start, A_column_index, A_value,
u, z);
if(check){ std::free(working_vectors); return check; }
double denom=two_norm_squared(m, u);
if(denom==0){ std::free(working_vectors); return QUERN_INPUT_ERROR; }
double alpha=rho/denom;
add_scaled(n, x, alpha, s);
add_scaled(n, r, -alpha, z);
++*return_iterations;
*return_residual_norm=two_norm(n, r);
if(*return_residual_norm<=absolute_convergence_tolerance){
*return_solved=1;
break;
}
if(*return_iterations>max_iterations)
break;
std::memcpy(u, r, n*sizeof(double));
check=QUERN_solve_with_r_transpose_in_place(n, R_row_start,
R_column_index, R_value, u);
if(check){ std::free(working_vectors); return check; }
check=QUERN_solve_with_r(n, R_row_start, R_column_index, R_value, u, z);
if(check){ std::free(working_vectors); return check; }
double rho_new=two_norm_squared(n, u);
double beta=rho_new/rho;
scale_and_add(n, beta, s, z);
rho=rho_new;
}
std::free(working_vectors);
return QUERN_OK;
}
