anchor.diff:           xmid, ymid, zmin, &
            x_inclination, y_inclination, z_inclination, &
            x_shear, y_shear, z_shear, &
  -         0.0, "  revolution")
  +         0.0_plflt, "  revolution")
      enddo
   
      ! x = xmax.
  -   call plschr(0., 1.0)
  +   call plschr(0._plflt, 1.0_plflt)
      do i = 1,NREVOLUTION
  -      omega = 2.*PI*((i-1)/(PLFLT)NREVOLUTION)
  +      omega = 2.*PI*((i-1)/dble(NREVOLUTION))
         sin_omega = sin(omega)
         cos_omega = cos(omega)
         x_inclination = 0.
  
positive.code:    real(PLFLT), dimension(:), allocatable   :: x, y
     real(PLFLT), dimension(:,:), allocatable :: z
  
     real(PLFLT) :: xmin=0., xmax=1.0, xmid = 0.5*(xmax + xmin), xrange = xmax - xmin, &
                    ymin=0., ymax=1.0, ymid = 0.5*(ymax + ymin), yrange = ymax - ymin, &
                    zmin=0., zmax=1.0, zmid = 0.5*(zmax + zmin), zrange = zmax - zmin, &
                    x_inclination, y_inclination, z_inclination,                       &
                    x_shear, y_shear, z_shear,                                         &
                    omega, sin_omega, cos_omega, domega
     integer     :: i, j
     real(PLFLT) :: radius, pitch, xpos, ypos, zpos
  
     character(len=1)  :: p1string = "O"
     character(len=80) :: pstring  = &
       *pstring = "The future of our civilization depends on software freedom."
  
     ! Allocate and define the minimal x, y, and z to insure 3D box
     allocate( x(XPTS) )
  
negative.code:                "bcd", "", zmax-zmin, 0)
  
     ! y = ymax.
     call plschr(0.0_plflt, 1.0_plflt)
     x_inclination = 1.
     y_inclination = 0.
     z_inclination = 0.
     x_shear = 0.
     do i = 1,NROTATION
        omega = 2.*PI*(i-1)/dble(NROTATION)
        sin_omega = sin(omega)
        cos_omega = cos(omega)
        y_shear = 0.5*yrange*sin_omega
        z_shear = 0.5*zrange*cos_omega
        call plptex3( &
           xmid, ymax, zmax -(zmax-0.2)*(dble(i-1)/dble(NROTATION-1)), &
           x_inclination, y_inclination, z_inclination, &
           x_shear, y_shear, z_shear, &
           0.5_plflt, "rotation for y = y#dmax#u")
     enddo
  
     ! x = xmax.
     call plschr(0.0_plflt, 1.0_plflt)
     x_inclination = 0.0
     y_inclination = -1.0
     z_inclination = 0.0
     y_shear = 0.0
     do i = 1,NROTATION
        omega = 2.*PI*((i-1)/dble(NROTATION))
        sin_omega = sin(omega)
        cos_omega = cos(omega)
        x_shear = 0.5*xrange*sin_omega
        z_shear = 0.5*zrange*cos_omega
        call plptex3( &
           xmax, ymid, zmax -(zmax-0.2)*((i-1)/dble(NROTATION-1)), &
           x_inclination, y_inclination, z_inclination, &
           x_shear, y_shear, z_shear, &
           0.5_plflt, "rotation for x = x#dmax#u")
     enddo
  
     ! z = zmin.
     call plschr(0.0_plflt, 1.0_plflt)
     x_inclination = 1.
     y_inclination = 0.
     z_inclination = 0.
     x_shear = 0.
     do i = 1,NROTATION
        omega = 2.*PI*((i-1)/dble(NROTATION))
        sin_omega = sin(omega)
        cos_omega = cos(omega)
        y_shear = 0.5*yrange*cos_omega
        z_shear = 0.5*zrange*sin_omega
        call plptex3( &
           xmid, ymax -(ymax-0.2)*(dble(i)/dble(NROTATION-1)), zmin, &
           x_inclination, y_inclination, z_inclination, &
           x_shear, y_shear, z_shear, &
           0.5_plflt, "rotation for z = z#dmin#u")
     enddo
     ! Draw minimal 3D grid to finish defining the 3D box.
     call plmesh(x, y, z, DRAW_LINEXY)
  
     ! Page 3: Demonstrate shear of string along its axis.
     ! Work around xcairo and pngcairo (but not pscairo) problems for
  