subroutine sgesl(a,lda,n,ipvt,b,job) integer lda,n,ipvt(1),job real a(lda,1),b(1) c c sgesl solves the real system c a * x = b or trans(a) * x = b c using the factors computed by sgeco or sgefa. c c on entry c c a real(lda, n) c the output from sgeco or sgefa. 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 ipvt integer(n) c the pivot vector from sgeco or sgefa. c c b real(n) c the right hand side vector. c c job integer c = 0 to solve a*x = b , c = nonzero to solve trans(a)*x = b where c trans(a) is the transpose. c c on return c c b the solution vector x . c c error condition c c a division by zero will occur if the input factor contains a c zero on the diagonal. technically this indicates singularity c but it is often caused by improper arguments or improper c setting of lda . it will not occur if the subroutines are c called correctly and if sgeco has set rcond .gt. 0.0 c or sgefa has set info .eq. 0 . c c to compute inverse(a) * c where c is a matrix c with p columns c call sgeco(a,lda,n,ipvt,rcond,z) c if (rcond is too small) go to ... c do 10 j = 1, p c call sgesl(a,lda,n,ipvt,c(1,j),0) c 10 continue 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,sdot c c internal variables c real sdot,t integer k,kb,l,nm1 c nm1 = n - 1 if (job .ne. 0) go to 50 c c job = 0 , solve a * x = b c first solve l*y = b c if (nm1 .lt. 1) go to 30 do 20 k = 1, nm1 l = ipvt(k) t = b(l) if (l .eq. k) go to 10 b(l) = b(k) b(k) = t 10 continue call saxpy(n-k,t,a(k+1,k),1,b(k+1),1) 20 continue 30 continue c c now solve u*x = y c do 40 kb = 1, n k = n + 1 - kb b(k) = b(k)/a(k,k) t = -b(k) call saxpy(k-1,t,a(1,k),1,b(1),1) 40 continue go to 100 50 continue c c job = nonzero, solve trans(a) * x = b c first solve trans(u)*y = b c do 60 k = 1, n t = sdot(k-1,a(1,k),1,b(1),1) b(k) = (b(k) - t)/a(k,k) 60 continue c c now solve trans(l)*x = y c if (nm1 .lt. 1) go to 90 do 80 kb = 1, nm1 k = n - kb b(k) = b(k) + sdot(n-k,a(k+1,k),1,b(k+1),1) l = ipvt(k) if (l .eq. k) go to 70 t = b(l) b(l) = b(k) b(k) = t 70 continue 80 continue 90 continue 100 continue return end