SUBROUTINE zbrak(fx,x1,x2,n,xb1,xb2,nb)
INTEGER n,nb
REAL x1,x2,xb1(nb),xb2(nb),fx
EXTERNAL fx
INTEGER i,nbb
REAL dx,fc,fp,x
nbb=0
x=x1
dx=(x2-x1)/n
fp=fx(x)
do i=1,n
  x=x+dx
  fc=fx(x)
  if(fc*fp<=0.) then
    nbb=nbb+1
    xb1(nbb)=x-dx
    xb2(nbb)=x
    if(nbb==nb) return
  endif
  fp=fc
end do
nb=nbb
END SUBROUTINE zbrak