program mandelbrot2

complex z,kappa
integer green,blue,i,j,k,loop

integer   N,maxiter
parameter (N=2000,maxiter=1000)
real      x(0:N*N-1)
    
! ----------------------------------------------------------------

do loop=0,N*N-1
    i=mod(loop,N)        ! i varies from 0 to N-1
    j=int(loop/N)        ! j varies from 0 to N-1
    kappa = cmplx((4.0*(i-N/2)/N),(4.0*(j-N/2)/N))

    k=1
    z=kappa
    do while (abs(z).le.2 .and. k.lt.maxiter) 
        k=k+1
        z=z*z + kappa
    end do

    x(loop)=log(real(k))/log(real(maxiter))
end do
 
! ----------------------------------------------------------------

write(6,*) 'Writing mandelbrot.ppm'

open(7,file='mandelbrot.ppm',status='unknown')
write(7,100) 'P6', N, N, 255

do loop=0,N*N-1
    if (x(loop).lt.0.5) then
        green=2.0*x(loop)*255
        write(7,110) achar(255-green),achar(green),achar(0)
    else 
        blue= 2.0*x(loop)*255 - 255
        write(7,110) achar(0),achar(255-blue),achar(blue)
    end if
end do

100  format(A2,/,I4,I5,/,I3)
110  format(3A1,$)

close(7)
end