How to make use of cosine Function to make this shape

[1988]

program Make_2D_Model
	implicit none
	integer : x,y
        integer:: i,j,nx,nz 
       integer :: idepth
  character*1,allocatable,dimension(:,:) :: icode

nx=1000  
nz=500
idepth=100
 x= !
 y=   !
	allocate(icode(1:nx,1:nz))	
	do i=1,nx
		do j=1,nz
			if(j<=idepth)then
				icode(i,j)='1'
			elseif(j>idepth)then
				icode(i,j)='3'		
            endif
		enddo
    enddo

    do i=1,nx
        do j=1,nz
            if  x= np.arange(0,3*np.pi,0.01)then
                icode(i,j)='2'
            endif
        enddo
    enddo


open(2012,file='model.txt',status='unknown')
		do j=1,nz
			write(2012,1000)(icode(i,j),i=1,nx)
		enddo
	close(2012)
	1000 format(<nx>a1)

    end program Make_2D_Model