subroutine sppdi(ap,n,det,job) integer n,job real ap(1) real det(2) c c sppdi computes the determinant and inverse c of a real symmetric positive definite matrix c using the factors computed by sppco or sppfa . c c on entry c c ap real (n*(n+1)/2) c the output from sppco or sppfa. c c n integer c the order of the matrix a . c c job integer c = 11 both determinant and inverse. c = 01 inverse only. c = 10 determinant only. c c on return c c ap the upper triangular half of the inverse . c the strict lower triangle is unaltered. c c det real(2) c determinant of original matrix if requested. c otherwise not referenced. c determinant = det(1) * 10.0**det(2) c with 1.0 .le. det(1) .lt. 10.0 c or det(1) .eq. 0.0 . c c error condition c c a division by zero will occur if the input factor contains c a zero on the diagonal and the inverse is requested. c it will not occur if the subroutines are called correctly c and if spoco or spofa has set info .eq. 0 . 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 blas saxpy,sscal c fortran mod c c internal variables c real t real s integer i,ii,j,jj,jm1,j1,k,kj,kk,kp1,k1 c c compute determinant c if (job/10 .eq. 0) go to 70 det(1) = 1.0e0 det(2) = 0.0e0 s = 10.0e0 ii = 0 do 50 i = 1, n ii = ii + i det(1) = ap(ii)**2*det(1) c ...exit if (det(1) .eq. 0.0e0) go to 60 10 if (det(1) .ge. 1.0e0) go to 20 det(1) = s*det(1) det(2) = det(2) - 1.0e0 go to 10 20 continue 30 if (det(1) .lt. s) go to 40 det(1) = det(1)/s det(2) = det(2) + 1.0e0 go to 30 40 continue 50 continue 60 continue 70 continue c c compute inverse(r) c if (mod(job,10) .eq. 0) go to 140 kk = 0 do 100 k = 1, n k1 = kk + 1 kk = kk + k ap(kk) = 1.0e0/ap(kk) t = -ap(kk) call sscal(k-1,t,ap(k1),1) kp1 = k + 1 j1 = kk + 1 kj = kk + k if (n .lt. kp1) go to 90 do 80 j = kp1, n t = ap(kj) ap(kj) = 0.0e0 call saxpy(k,t,ap(k1),1,ap(j1),1) j1 = j1 + j kj = kj + j 80 continue 90 continue 100 continue c c form inverse(r) * trans(inverse(r)) c jj = 0 do 130 j = 1, n j1 = jj + 1 jj = jj + j jm1 = j - 1 k1 = 1 kj = j1 if (jm1 .lt. 1) go to 120 do 110 k = 1, jm1 t = ap(kj) call saxpy(k,t,ap(j1),1,ap(k1),1) k1 = k1 + k kj = kj + 1 110 continue 120 continue t = ap(jj) call sscal(j,t,ap(j1),1) 130 continue 140 continue return end