subroutine cctslz(a,x,r,m,l,k,lda)
integer m,l,k,lda
double complex a(lda,k),x(m,l,k),r(1)
c
c cctslz solves the double complex linear system
c a * x = b
c with the cct - matrix a .
c
c on entry
c
c a double complex((2*m - 1)*l,k)
c the first row of outer blocks of the cct - matrix .
c each outer block is represented by its first row
c of inner blocks. each inner block is represented
c by its first row followed by its first column
c beginning with the second element .
c on return a has been destroyed .
c
c x double complex(m*l*k)
c the right hand side vector b .
c
c r double complex(max(2*m - 2,2*l,2*k))
c a work vector .
c
c m integer
c the order of the inner blocks of the matrix a .
c
c l integer
c the number of inner blocks in a row or column
c of an outer block of the matrix a .
c
c k integer
c the number of outer blocks in a row or column
c of the matrix a .
c
c lda integer
c the leading dimension of the array a .
c
c on return
c
c x the solution vector .
c
c toeplitz package. this version dated 07/23/82 .
c
c subroutines and functions
c
c toeplitz package ... ctslz,salwz
c fortran ... dfloat
c
c internal variables
c
integer i1,i2,i3,m2,ml
double precision rk
c
rk = dfloat(k)
m2 = 2*m - 1
ml = m*l
c
c reduce the cct - matrix to a block-diagonal matrix
c by the inverse discrete fourier transformation .
c
call salwz(a,r,r(k+1),m2*l,k,lda,-1)
c
c compute the discrete fourier transformation of
c the right hand side vector .
c
call salwz(x,r,r(k+1),ml,k,ml,1)
c
c solve the block-diagonal system, blocks of which
c are ct - matrices .
c
do 10 i3 = 1, k
call ctslz(a(1,i3),x(1,1,i3),r,m,l,m2)
10 continue
c
c compute the solution of the given system by
c the inverse discrete fourier transformation .
c
call salwz(x,r,r(k+1),ml,k,ml,-1)
c
do 40 i3 = 1, k
do 30 i2 = 1, l
do 20 i1 = 1, m
x(i1,i2,i3) = x(i1,i2,i3)/rk
20 continue
30 continue
40 continue
return
end