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arpack-ng/EXAMPLES/BAND/cnbdr2.f
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wo80 0eaf38bd51 Fix examples BAND _nbdr2 returning error info = -9 
Both examples access the M matrix, so we initialize M to be the identity matrix. See #443 for discussion.
2023-12-20 09:41:27 +01:00

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program cnbdr2
c
c ... Construct the matrix A in LAPACK-style band form.
c The matrix A is derived from the discretization of
c the 2-d convection-diffusion operator
c
c -Laplacian(u) + rho*partial(u)/partial(x).
c
c on the unit square with zero Dirichlet boundary condition
c using standard central difference.
c
c ... Call CNBAND to find eigenvalues LAMBDA such that
c A*x = x*LAMBDA.
c
c ... Use mode 3 of CNAUPD.
c
c\BeginLib
c
c cnband ARPACK banded eigenproblem solver.
c slapy2 LAPACK routine to compute sqrt(x**2+y**2) carefully.
c claset LAPACK routine to initialize a matrix to zero.
c caxpy Level 1 BLAS that computes y <- alpha*x+y.
c scnrm2 Level 1 BLAS that computes the norm of a vector.
c cgbmv Level 2 BLAS that computes the band matrix vector product
c
c\Author
c Richard Lehoucq
c Danny Sorensen
c Chao Yang
c Dept. of Computational &
c Applied Mathematics
c Rice University
c Houston, Texas
c
c\SCCS Information: @(#)
c FILE: nbdr2.F SID: 2.4 DATE OF SID: 10/20/00 RELEASE: 2
c
c\Remarks
c 1. None
c
c\EndLib
c
c----------------------------------------------------------------------
c
c %-------------------------------------%
c | Define leading dimensions for all |
c | arrays. |
c | MAXN - Maximum size of the matrix |
c | MAXNEV - Maximum number of |
c | eigenvalues to be computed |
c | MAXNCV - Maximum number of Arnoldi |
c | vectors stored |
c | MAXBDW - Maximum bandwidth |
c %-------------------------------------%
c
integer maxn, maxnev, maxncv, maxbdw, lda,
& lworkl, ldv
parameter ( maxn = 1000, maxnev = 25, maxncv=50,
& maxbdw=50, lda = maxbdw, ldv = maxn )
c
c %--------------%
c | Local Arrays |
c %--------------%
c
integer iparam(11), iwork(maxn)
logical select(maxncv)
Complex
& a(lda,maxn), m(lda,maxn), fac(lda,maxn),
& workl(3*maxncv*maxncv+5*maxncv), workd(3*maxn),
& workev(2*maxncv), v(ldv, maxncv),
& resid(maxn), d(maxncv), ax(maxn)
Real
& rwork(maxn), rd(maxncv,3)
c
c %---------------%
c | Local Scalars |
c %---------------%
c
character which*2, bmat
integer nev, ncv, kl, ku, info, i, j,
& n, nxi, lo, isub, isup, idiag, maxitr, mode,
& nconv
logical rvec
Real
& tol
Complex
& rho, h, h2, sigma
c
c %------------%
c | Parameters |
c %------------%
c
Complex
& one, zero, two
parameter (one = (1.0E+0, 0.0E+0) ,
& zero = (0.0E+0, 0.0E+0) ,
& two = (2.0E+0, 0.0E+0) )
c
c %-----------------------------%
c | BLAS & LAPACK routines used |
c %-----------------------------%
c
Real
& scnrm2, slapy2
external scnrm2, cgbmv, caxpy, slapy2, claset
c
c %-----------------------%
c | Executable Statements |
c %-----------------------%
c
c %-------------------------------------------------%
c | The number NX is the number of interior points |
c | in the discretization of the 2-dimensional |
c | convection-diffusion operator on the unit |
c | square with zero Dirichlet boundary condition. |
c | The number N(=NX*NX) is the dimension of the |
c | matrix. A standard eigenvalue problem is |
c | solved (BMAT = 'I'). NEV is the number of |
c | eigenvalues (closest to SIGMA) to be |
c | approximated. Since the shift and invert mode |
c | is used, WHICH is set to 'LM'. The user can |
c | modify NX, NEV and NCV to solve problems of |
c | different sizes, and to get different parts the |
c | spectrum. However, the following conditions |
c | must be satisfied: |
c | N <= MAXN |
c | NEV <= MAXNEV |
c | NEV + 2 <= NCV <= MAXNCV |
c %-------------------------------------------------%
c
nxi = 10
n = nxi*nxi
nev = 4
ncv = 10
if ( n .gt. maxn ) then
print *, ' ERROR with _NBDR2: N is greater than MAXN '
go to 9000
else if ( nev .gt. maxnev ) then
print *, ' ERROR with _NBDR2: NEV is greater than MAXNEV '
go to 9000
else if ( ncv .gt. maxncv ) then
print *, ' ERROR with _NBDR2: NCV is greater than MAXNCV '
go to 9000
end if
bmat = 'I'
which = 'LM'
sigma = zero
c
c %-----------------------------------------------------%
c | The work array WORKL is used in CNAUPD as |
c | workspace. Its dimension LWORKL is set as |
c | illustrated below. The parameter TOL determines |
c | the stopping criterion. If TOL<=0, machine |
c | precision is used. Setting INFO=0 indicates that a |
c | random vector is generated in CNAUPD to start the |
c | Arnoldi iteration. |
c %-----------------------------------------------------%
c
lworkl = 3*ncv**2+5*ncv
tol = 0.0
info = 0
c
c %---------------------------------------------------%
c | IPARAM(3) specifies the maximum number of Arnoldi |
c | iterations allowed. Mode 3 of CNAUPD is used |
c | (IPARAM(7) = 3). All these options can be changed |
c | by the user. For details, see the documentation |
c | in cnband. |
c %---------------------------------------------------%
c
maxitr = 300
mode = 3
c
iparam(3) = maxitr
iparam(7) = mode
c
c %----------------------------------------%
c | Construct the matrix A in LAPACK-style |
c | banded form. |
c %----------------------------------------%
c
c %---------------------------------------------%
c | Zero out the workspace for banded matrices. |
c %---------------------------------------------%
c
call claset('A', lda, n, zero, zero, a, lda)
call claset('A', lda, n, zero, zero, m, lda)
call claset('A', lda, n, zero, zero, fac, lda)
c
c %-------------------------------------%
c | KU, KL are number of superdiagonals |
c | and subdiagonals within the band of |
c | matrices A and M. |
c %-------------------------------------%
c
kl = nxi
ku = nxi
c
c %---------------%
c | Main diagonal |
c %---------------%
c
h = one / cmplx(nxi+1)
h2 = h*h
c
idiag = kl+ku+1
do 30 j = 1, n
a(idiag,j) = (4.0E+0, 0.0E+0) / h2
m(idiag,j) = (1.0E+0, 0.0E+0)
30 continue
c
c %-------------------------------------%
c | First subdiagonal and superdiagonal |
c %-------------------------------------%
c
rho = (1.0E+2, 0.0E+0)
isup = kl+ku
isub = kl+ku+2
do 50 i = 1, nxi
lo = (i-1)*nxi
do 40 j = lo+1, lo+nxi-1
a(isup,j+1) = -one/h2 + rho/two/h
a(isub,j) = -one/h2 - rho/two/h
40 continue
50 continue
c
c %------------------------------------%
c | KL-th subdiagonal and KU-th super- |
c | diagonal. |
c %------------------------------------%
c
isup = kl+1
isub = 2*kl+ku+1
do 80 i = 1, nxi-1
lo = (i-1)*nxi
do 70 j = lo+1, lo+nxi
a(isup,nxi+j) = -one / h2
a(isub,j) = -one / h2
70 continue
80 continue
c
c %-----------------------------------------------%
c | Call ARPACK banded solver to find eigenvalues |
c | and eigenvectors. Eigenvalues are returned in |
c | the one dimensional array D. Eigenvectors |
c | are returned in the first NCONV (=IPARAM(5)) |
c | columns of V. |
c %-----------------------------------------------%
c
rvec = .true.
call cnband(rvec, 'A', select, d, v, ldv, sigma,
& workev, n, a, m, lda, fac, kl, ku, which,
& bmat, nev, tol, resid, ncv, v, ldv, iparam,
& workd, workl, lworkl, rwork, iwork, info)
c
if ( info .eq. 0) then
c
nconv = iparam(5)
c
c %-----------------------------------%
c | Print out convergence information |
c %-----------------------------------%
c
print *, ' '
print *, '_NBDR2 '
print *, '====== '
print *, ' '
print *, ' The size of the matrix is ', n
print *, ' Number of eigenvalue requested is ', nev
print *, ' The number of Arnoldi vectors generated',
& ' (NCV) is ', ncv
print *, ' The number of converged Ritz values is ',
& nconv
print *, ' What portion of the spectrum ', which
print *, ' The number of Implicit Arnoldi ',
& ' update taken is ', iparam(3)
print *, ' The number of OP*x is ', iparam(9)
print *, ' The convergence tolerance is ', tol
print *, ' '
c
c %----------------------------%
c | Compute the residual norm. |
c | || A*x - lambda*x || |
c %----------------------------%
c
do 90 j = 1, nconv
c
c %---------------------------%
c | Compute the residual norm |
c | || A*x - lambda*x || |
c %---------------------------%
c
call cgbmv('Notranspose', n, n, kl, ku, one,
& a(kl+1,1), lda, v(1,j), 1, zero,
& ax, 1)
call caxpy(n, -d(j), v(1,j), 1, ax, 1)
rd(j,1) = real (d(j))
rd(j,2) = aimag(d(j))
rd(j,3) = scnrm2(n, ax, 1)
rd(j,3) = rd(j,3) / slapy2(rd(j,1),rd(j,2))
90 continue
call smout(6, nconv, 3, rd, maxncv, -6,
& 'Ritz values (Real,Imag) and relative residuals')
else
c
c %-------------------------------------%
c | Either convergence failed, or there |
c | is error. Check the documentation |
c | for cnband. |
c %-------------------------------------%
c
print *, ' '
print *, ' Error with _nband, info= ', info
print *, ' Check the documentation of _nband '
print *, ' '
c
end if
c
9000 end
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