subroutine cpoco(a,lda,n,rcond,z,info) integer lda,n,info complex a(lda,1),z(1) real rcond c c cpoco factors a complex hermitian positive definite matrix c and estimates the condition of the matrix. c c if rcond is not needed, cpofa is slightly faster. c to solve a*x = b , follow cpoco by cposl. c to compute inverse(a)*c , follow cpoco by cposl. c to compute determinant(a) , follow cpoco by cpodi. c to compute inverse(a) , follow cpoco by cpodi. c c on entry c c a complex(lda, n) c the hermitian matrix to be factored. only the c diagonal and upper triangle are used. c c lda integer c the leading dimension of the array a . c c n integer c the order of the matrix a . c c on return c c a an upper triangular matrix r so that a = c ctrans(r)*r where ctrans(r) is the conjugate c transpose. the strict lower triangle is unaltered. c if info .ne. 0 , the factorization is not complete. c c rcond real c an estimate of the reciprocal condition of a . c for the system a*x = b , relative perturbations c in a and b of size epsilon may cause c relative perturbations in x of size epsilon/rcond . c if rcond is so small that the logical expression c 1.0 + rcond .eq. 1.0 c is true, then a may be singular to working c precision. in particular, rcond is zero if c exact singularity is detected or the estimate c underflows. if info .ne. 0 , rcond is unchanged. c c z complex(n) c a work vector whose contents are usually unimportant. c if a is close to a singular matrix, then z is c an approximate null vector in the sense that c norm(a*z) = rcond*norm(a)*norm(z) . c if info .ne. 0 , z is unchanged. c c info integer c = 0 for normal return. c = k signals an error condition. the leading minor c of order k is not positive definite. c c linpack. this version dated 08/14/78 . c cleve moler, university of new mexico, argonne national lab. c c subroutines and functions c c linpack cpofa c blas caxpy,cdotc,csscal,scasum c fortran abs,aimag,amax1,cmplx,conjg,real c c internal variables c complex cdotc,ek,t,wk,wkm real anorm,s,scasum,sm,ynorm integer i,j,jm1,k,kb,kp1 c complex zdum,zdum2,csign1 real cabs1 cabs1(zdum) = abs(real(zdum)) + abs(aimag(zdum)) csign1(zdum,zdum2) = cabs1(zdum)*(zdum2/cabs1(zdum2)) c c find norm of a using only upper half c do 30 j = 1, n z(j) = cmplx(scasum(j,a(1,j),1),0.0e0) jm1 = j - 1 if (jm1 .lt. 1) go to 20 do 10 i = 1, jm1 z(i) = cmplx(real(z(i))+cabs1(a(i,j)),0.0e0) 10 continue 20 continue 30 continue anorm = 0.0e0 do 40 j = 1, n anorm = amax1(anorm,real(z(j))) 40 continue c c factor c call cpofa(a,lda,n,info) if (info .ne. 0) go to 180 c c rcond = 1/(norm(a)*(estimate of norm(inverse(a)))) . c estimate = norm(z)/norm(y) where a*z = y and a*y = e . c the components of e are chosen to cause maximum local c growth in the elements of w where ctrans(r)*w = e . c the vectors are frequently rescaled to avoid overflow. c c solve ctrans(r)*w = e c ek = (1.0e0,0.0e0) do 50 j = 1, n z(j) = (0.0e0,0.0e0) 50 continue do 110 k = 1, n if (cabs1(z(k)) .ne. 0.0e0) ek = csign1(ek,-z(k)) if (cabs1(ek-z(k)) .le. real(a(k,k))) go to 60 s = real(a(k,k))/cabs1(ek-z(k)) call csscal(n,s,z,1) ek = cmplx(s,0.0e0)*ek 60 continue wk = ek - z(k) wkm = -ek - z(k) s = cabs1(wk) sm = cabs1(wkm) wk = wk/a(k,k) wkm = wkm/a(k,k) kp1 = k + 1 if (kp1 .gt. n) go to 100 do 70 j = kp1, n sm = sm + cabs1(z(j)+wkm*conjg(a(k,j))) z(j) = z(j) + wk*conjg(a(k,j)) s = s + cabs1(z(j)) 70 continue if (s .ge. sm) go to 90 t = wkm - wk wk = wkm do 80 j = kp1, n z(j) = z(j) + t*conjg(a(k,j)) 80 continue 90 continue 100 continue z(k) = wk 110 continue s = 1.0e0/scasum(n,z,1) call csscal(n,s,z,1) c c solve r*y = w c do 130 kb = 1, n k = n + 1 - kb if (cabs1(z(k)) .le. real(a(k,k))) go to 120 s = real(a(k,k))/cabs1(z(k)) call csscal(n,s,z,1) 120 continue z(k) = z(k)/a(k,k) t = -z(k) call caxpy(k-1,t,a(1,k),1,z(1),1) 130 continue s = 1.0e0/scasum(n,z,1) call csscal(n,s,z,1) c ynorm = 1.0e0 c c solve ctrans(r)*v = y c do 150 k = 1, n z(k) = z(k) - cdotc(k-1,a(1,k),1,z(1),1) if (cabs1(z(k)) .le. real(a(k,k))) go to 140 s = real(a(k,k))/cabs1(z(k)) call csscal(n,s,z,1) ynorm = s*ynorm 140 continue z(k) = z(k)/a(k,k) 150 continue s = 1.0e0/scasum(n,z,1) call csscal(n,s,z,1) ynorm = s*ynorm c c solve r*z = v c do 170 kb = 1, n k = n + 1 - kb if (cabs1(z(k)) .le. real(a(k,k))) go to 160 s = real(a(k,k))/cabs1(z(k)) call csscal(n,s,z,1) ynorm = s*ynorm 160 continue z(k) = z(k)/a(k,k) t = -z(k) call caxpy(k-1,t,a(1,k),1,z(1),1) 170 continue c make znorm = 1.0 s = 1.0e0/scasum(n,z,1) call csscal(n,s,z,1) ynorm = s*ynorm c if (anorm .ne. 0.0e0) rcond = ynorm/anorm if (anorm .eq. 0.0e0) rcond = 0.0e0 180 continue return end