code: def mouse_zoom(self, inc):
          '''Convenience function to implement a zoom function.
  
          This is achieved by moving ``Camera.position`` in the
          direction of the ``Camera.c`` vector.
  
          '''
          # Square Distance from pivot
          dsq = np.linalg.norm(self.position - self.pivot)
          minsq = 1.0**2  # How near can we be to the pivot
          maxsq = 7.0**2 # How far can we go 
  
          scalefac = 0.25
  
          if dsq > maxsq and inc < 0: 
              # We're going too far
              pass
          elif dsq < minsq and inc > 0:
              # We're going too close
              pass
          else:
              # We're golden
              self.position += self.c*inc*scalefaf mouse_zoom(self, inc):
          '''Convenience function to implement a zoom function.
  
          This is achieved by moving ``Camera.position`` in the
          direction of the ``Camera.c`` vector.
  
          '''
          # Square Distance from pivot
          dsq = np.linalg.norm(self.position - self.pivot)
          minsq = 1.0**2  # How near can we be to the pivot
          maxsq = 7.0**2 # How far can we go 
  
          scalefac = 0.25
  
          if dsq > maxsq and inc < 0: 
              # We're going too far
              pass
          elif dsq < minsq and inc > 0:
              # We're going too close
              pass
          else:
              # We're golden
              self.position += self.c*inc*scalefac
docs: Convenience function to implement a zoom function.
  
          This is achieved by moving ``Camera.position`` in the
          direction of the ``Camera.c`` vector.