f08fece.c

/* nag_lapackeig_dsytrd (f08fec) Example Program.
 *
 * Copyright 2025 Numerical Algorithms Group.
 *
 * Mark 31.1, 2025.
 */
#include<nag.h>
#include<stdio.h>
intmain(void){
/* Scalars */
Integeri,j,n,pda,pdz,d_len,e_len,tau_len;
Integerexit_status=0;
NagErrorfail;
Nag_UploTypeuplo;
Nag_OrderTypeorder;
/* Arrays */
charnag_enum_arg[40];
double*a=0,*d=0,*e=0,*tau=0,*z=0;
#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_dsytrd (f08fec) Example Program Results\n\n");
/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%"NAG_IFMT"%*[^\n] ",&n);
pda=n;
pdz=n;
tau_len=n-1;
d_len=n;
e_len=n-1;
/* Allocate memory */
if(!(a=NAG_ALLOC(n*n,double))||!(d=NAG_ALLOC(d_len,double))||
!(e=NAG_ALLOC(e_len,double))||!(tau=NAG_ALLOC(tau_len,double))||
!(z=NAG_ALLOC(n*n,double))){
printf("Allocation failure\n");
exit_status=-1;
gotoEND;
}
/* Read A from data file */
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);
if(uplo==Nag_Upper){
for(i=1;i<=n;++i){
for(j=i;j<=n;++j)
scanf("%lf",&A(i,j));
}
scanf("%*[^\n] ");
}else{
for(i=1;i<=n;++i){
for(j=1;j<=i;++j)
scanf("%lf",&A(i,j));
}
scanf("%*[^\n] ");
}
/* Reduce A to tridiagonal form T = (Q^T)*A*Q */
/* nag_lapackeig_dsytrd (f08fec).
 * Orthogonal reduction of real symmetric matrix to
 * symmetric tridiagonal form
 */
nag_lapackeig_dsytrd(order,uplo,n,a,pda,d,e,tau,&fail);
if(fail.code!=NE_NOERROR){
printf("Error from nag_lapackeig_dsytrd (f08fec).\n%s\n",fail.message);
exit_status=1;
}
/* Copy A into Z using nag_blast_dtr_copy (f16qec). */
nag_blast_dtr_copy(order,uplo,Nag_NoTrans,Nag_NonUnitDiag,n,a,pda,z,
pdz,&fail);
if(fail.code!=NE_NOERROR){
printf("Error from dtr_copy.\n%s\n",fail.message);
exit_status=1;
gotoEND;
}
/* Form Q explicitly, storing the result in z using nag_lapackeig_dorgtr
 * (f08ffc). */
nag_lapackeig_dorgtr(order,uplo,n,z,pdz,tau,&fail);
if(fail.code!=NE_NOERROR){
printf("Error from nag_lapackeig_dorgtr (f08ffc).\n%s\n",fail.message);
exit_status=1;
gotoEND;
}
/* Calculate all the eigenvalues and eigenvectors of matrix A */
nag_lapackeig_dsteqr(order,Nag_UpdateZ,n,d,e,z,pdz,&fail);
if(fail.code!=NE_NOERROR){
printf("Error from nag_lapackeig_dsteqr (f08jec).\n%s\n",fail.message);
exit_status=1;
gotoEND;
}
/* Normalize the eigenvectors */
for(j=1;j<=n;j++){
for(i=n;i>=1;i--){
Z(i,j)=Z(i,j)/Z(1,j);
}
}
/* Print eigenvalues and eigenvectors */
printf("Eigenvalues\n");
for(i=1;i<=n;++i)
printf("%8.4f%s",d[i-1],i%8==0?"\n":" ");
printf("\n\n");
/* nag_file_print_matrix_real_gen (x04cac).
 * Print real general matrix (easy-to-use)
 */
fflush(stdout);
nag_file_print_matrix_real_gen(order,Nag_GeneralMatrix,Nag_NonUnitDiag,n,
n,z,pdz,"Eigenvectors",0,&fail);
if(fail.code!=NE_NOERROR){
printf("Error from nag_file_print_matrix_real_gen (x04cac).\n%s\n",
fail.message);
exit_status=1;
gotoEND;
}
END:
NAG_FREE(a);
NAG_FREE(d);
NAG_FREE(e);
NAG_FREE(tau);
NAG_FREE(z);
returnexit_status;
}