f08fbce.c

/* nag_lapackeig_dsyevx (f08fbc) Example Program.
 *
 * Copyright 2025 Numerical Algorithms Group.
 *
 * Mark 31.1, 2025.
 */
#include<nag.h>
#include<stdio.h>
intmain(void){
/* Scalars */
doubleabstol,vl,vu;
Integeri,il=0,iu=0,j,m,n,pda,pdz;
Integerexit_status=0;
/* Arrays */
charnag_enum_arg[40];
double*a=0,*w=0,*z=0;
Integer*index=0;
/* Nag Types */
Nag_OrderTypeorder;
Nag_RangeTyperange;
Nag_UploTypeuplo;
Nag_JobTypejob;
NagErrorfail,fail_print;
#ifdef NAG_COLUMN_MAJOR
#define A(I, J) a[(J - 1) * pda + I - 1]
#define Z(I, J) z[(J - 1) * pdz + I - 1]
order=Nag_ColMajor;
#else
#define A(I, J) a[(I - 1) * pda + J - 1]
#define Z(I, J) z[(I - 1) * pdz + J - 1]
order=Nag_RowMajor;
#endif
INIT_FAIL(fail);
printf("nag_lapackeig_dsyevx (f08fbc) Example Program Results\n\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%"NAG_IFMT"%*[^\n]",&n);
/* Read uplo, range and job */
scanf("%39s%*[^\n]",nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
 * Converts NAG enum member name to value.
 */
uplo=(Nag_UploType)nag_enum_name_to_value(nag_enum_arg);
scanf("%39s%*[^\n]",nag_enum_arg);
range=(Nag_RangeType)nag_enum_name_to_value(nag_enum_arg);
scanf("%39s%*[^\n]",nag_enum_arg);
job=(Nag_JobType)nag_enum_name_to_value(nag_enum_arg);
/* Allocate memory */
if(!(a=NAG_ALLOC(n*n,double))||!(w=NAG_ALLOC(n,double))||
!(z=NAG_ALLOC(n*n,double))||!(index=NAG_ALLOC(n,Integer))){
printf("Allocation failure\n");
exit_status=-1;
gotoEND;
}
pda=n;
pdz=n;
/* Read the lower and upper bounds of the interval to be searched,
 * and read the upper triangular part of the matrix A from data file
 */
scanf("%lf%lf%*[^\n]",&vl,&vu);
for(i=1;i<=n;++i)
for(j=i;j<=n;++j)
scanf("%lf",&A(i,j));
scanf("%*[^\n]");
/* Set the absolute error tolerance for eigenvalues. With abstol
 * set to zero, the default value is used instead.
 */
abstol=0.0;
/* nag_lapackeig_dsyevx (f08fbc).
 * Solve the symmetric eigenvalue problem.
 */
nag_lapackeig_dsyevx(order,job,range,uplo,n,a,pda,vl,vu,il,iu,
abstol,&m,w,z,pdz,index,&fail);
if(fail.code!=NE_NOERROR&&fail.code!=NE_CONVERGENCE){
printf("Error from nag_lapackeig_dsyevx (f08fbc).\n%s\n",fail.message);
exit_status=1;
gotoEND;
}
/* Normalize the eigenvectors */
for(j=1;j<=m;j++)
for(i=n;i>=1;i--)
Z(i,j)=Z(i,j)/Z(1,j);
/* Print solution */
printf("Number of eigenvalues found =%5"NAG_IFMT"\n",m);
printf("\nEigenvalues\n");
for(j=0;j<m;++j)
printf("%8.4f%s",w[j],(j+1)%8==0?"\n":" ");
printf("\n\n");
/* nag_file_print_matrix_real_gen (x04cac).
 * Print selected eigenvectors.
 */
INIT_FAIL(fail_print);
fflush(stdout);
nag_file_print_matrix_real_gen(order,Nag_GeneralMatrix,Nag_NonUnitDiag,n,
m,z,pdz,"Selected eigenvectors",0,
&fail_print);
if(fail_print.code!=NE_NOERROR){
printf("Error from nag_file_print_matrix_real_gen (x04cac).\n%s\n",
fail_print.message);
exit_status=1;
gotoEND;
}
if(fail.code==NE_CONVERGENCE){
printf("eigenvectors failed to converge\n");
printf("Indices of eigenvectors that did not converge\n");
for(j=0;j<m;++j)
printf("%8"NAG_IFMT"%s",index[j],(j+1)%8==0?"\n":" ");
}
END:
NAG_FREE(a);
NAG_FREE(w);
NAG_FREE(z);
NAG_FREE(index);
returnexit_status;
}
#undef A
#undef Z