subroutine spbdi(abd,lda,n,m,det) integer lda,n,m real abd(lda,1) real det(2) c c spbdi computes the determinant c of a real symmetric positive definite band matrix c using the factors computed by spbco or spbfa. c if the inverse is needed, use spbsl n times. c c on entry c c abd real(lda, n) c the output from spbco or spbfa. c c lda integer c the leading dimension of the array abd . c c n integer c the order of the matrix a . c c m integer c the number of diagonals above the main diagonal. c c on return c c det real(2) c determinant of original matrix in the form 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 linpack. this version dated 08/14/78 . c cleve moler, university of new mexico, argonne national lab. c c subroutines and functions c c c internal variables c real s integer i c c compute determinant c det(1) = 1.0e0 det(2) = 0.0e0 s = 10.0e0 do 50 i = 1, n det(1) = abd(m+1,i)**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 return end