subroutine y12mfe(n,a,snr,nn,rnr,nn1,a1,sn,nz,ha,iha,b,b1,x,y,
1 aflag,iflag,ifail)
implicit real(a-b,d,g,p,t-y),integer(c,f,h-n,r-s,z)
double precision ext,er,er1,er2,err,e
real a(nn),b(n),b1(n),x(n),y(n),a1(nz),aflag(11)
integer snr(nn),rnr(nn1),ha(iha,13),sn(nz),iflag(12)
c
c store the non-zero elements,their column numbers,information about
c row starts,information about row ends and the right-hand side.
c
ifail=0
nres=0
dres=0.0
state=iflag(5)
kit=1
it=iflag(11)
if(state.eq.1)ifail=10
if(it.lt.2)ifail=23
if(ifail.ne.0)go to 160
do 10 i=1,n
10 b1(i)=b(i)
if(state.eq.3)go to 70
call y12mbe(n,nz,a,snr,nn,rnr,nn1,ha,iha,aflag,iflag,ifail)
if(ifail.ne.0)go to 160
do 20 i=1,nz
sn(i)=snr(i)
20 a1(i)=a(i)
do 30 i=1,n
ha(i,12)=ha(i,1)
30 ha(i,13)=ha(i,3)
if(aflag(2).ge.0.0)go to 60
gt1=aflag(6)
do 50 i=1,n
l1=ha(i,1)
l2=ha(i,3)
gt2=0.0
do 40 j=l1,l2
d=abs(a(j))
40 if(gt2.lt.d)gt2=d
50 if(gt2.lt.gt1)gt1=gt2
aflag(2)=-gt1*aflag(2)
c
c find the first solution.
c
60 call y12mce(n,nz,a,snr,nn,rnr,nn1,y,b,ha,iha,aflag,iflag,ifail)
if(ifail.ne.0)go to 160
70 call y12mde(n,a,nn,b,y,snr,ha,iha,iflag,ifail)
if(ifail.ne.0)go to 160
c
c prepare the data in order to begin the iterations.
c
dd=0.0
do 80 i=1,n
x(i)=b(i)
xx=abs(b(i))
80 if(dd.lt.xx)dd=xx
xm=dd
if(dd.eq.0.)go to 160
c
c begin to iterate.
c
90 d=dd
dres=0.
do 110 i=1,n
er=b1(i)
l1=ha(i,12)
l2=ha(i,13)
do 100 j=l1,l2
er1=a1(j)
l3=sn(j)
er2=x(l3)
100 er=er-er1*er2
c
c store residuals rounded to single precision.
c
b(i)=er
xx=dabs(er)
110 if(dres.lt.xx)dres=xx
if(dres.eq.0.)go to 160
if(nres.eq.1) go to 150
if(dres.gt.1.0e+4*xm)go to 150
kit=kit+1
iflag(5)=3
call y12mde(n,a,nn,b,y,snr,ha,iha,iflag,ifail)
if(ifail.ne.0)go to 160
c
c compute the uniform norm of the current solution vector.
c
dd=0.
do 120 i=1,n
xx=abs(b(i))
120 if(dd.lt.xx)dd=xx
if(dd.eq.0.0)go to 160
c
c check the convergence criterion.
c
if(dd.gt.d.and.kit.gt.2)go to 160
c
c calculate an improved solution.
c
dcor=dd
xm=0.0
do 130 i=1,n
x(i)=x(i)+b(i)
xx=abs(x(i))
130 if(xx.gt.xm) xm=xx
c
c check the stopping criteria.
c
if(10.0+dd/xm.eq.10.0) go to 140
if(kit.lt.it) go to 90
c
c end of the iterations.
c
140 nres=1
go to 90
150 dd=abs(dd)
160 iflag(5)=state
iflag(12)=kit
aflag(9)=dd
aflag(10)=dres
aflag(11)=xm
return
end
.
