interp_linear Subroutine

  subroutine interp_linear(x_table,y_table,n_table,x_itp,y_itp,n_itp)
    ! linear interpolation
    ! 1D method

    integer :: n_table,n_itp
    double precision :: x_table(n_table),y_table(n_table)
    double precision :: x_itp(n_itp),y_itp(n_itp)

    integer :: i,j

    !if (x_table(1)>x_itp(1) .or. x_table(n_table)<x_itp(n_itp)) then
    !  call mpistop("out of interpolation table")
    !endif

    do i=1,n_itp
      if(x_itp(i)<x_table(1)) then
        y_itp(i)=y_table(1)
        exit
      end if
      if(x_itp(i)>=x_table(n_table)) then
        y_itp(i)=y_table(n_table)
        exit
      end if
      LOOPT: do j=1,n_table-1
        if (x_itp(i)>=x_table(j) .and. x_itp(i)<x_table(j+1)) then
          y_itp(i)=y_table(j) + (x_itp(i)-x_table(j))*(y_table(j+&
             1)-y_table(j))/(x_table(j+1)-x_table(j))
          exit LOOPT
        endif
      enddo LOOPT
    enddo

  end subroutine interp_linear