subroutine eltran(nm,n,low,igh,a,int,z) c integer i,j,n,kl,mm,mp,nm,igh,low,mp1 double precision a(nm,igh),z(nm,n) integer int(igh) c c this subroutine is a translation of the algol procedure elmtrans, c num. math. 16, 181-204(1970) by peters and wilkinson. c handbook for auto. comp., vol.ii-linear algebra, 372-395(1971). c c this subroutine accumulates the stabilized elementary c similarity transformations used in the reduction of a c real general matrix to upper hessenberg form by elmhes. c c on input c c nm must be set to the row dimension of two-dimensional c array parameters as declared in the calling program c dimension statement. c c n is the order of the matrix. c c low and igh are integers determined by the balancing c subroutine balanc. if balanc has not been used, c set low=1, igh=n. c c a contains the multipliers which were used in the c reduction by elmhes in its lower triangle c below the subdiagonal. c c int contains information on the rows and columns c interchanged in the reduction by elmhes. c only elements low through igh are used. c c on output c c z contains the transformation matrix produced in the c reduction by elmhes. c c questions and comments should be directed to burton s. garbow, c mathematics and computer science div, argonne national laboratory c c this version dated august 1983. c c ------------------------------------------------------------------ c c .......... initialize z to identity matrix .......... do 80 j = 1, n c do 60 i = 1, n 60 z(i,j) = 0.0d0 c z(j,j) = 1.0d0 80 continue c kl = igh - low - 1 if (kl .lt. 1) go to 200 c .......... for mp=igh-1 step -1 until low+1 do -- .......... do 140 mm = 1, kl mp = igh - mm mp1 = mp + 1 c do 100 i = mp1, igh 100 z(i,mp) = a(i,mp-1) c i = int(mp) if (i .eq. mp) go to 140 c do 130 j = mp, igh z(mp,j) = z(i,j) z(i,j) = 0.0d0 130 continue c z(i,mp) = 1.0d0 140 continue c 200 return end