docstr: Apply this color scheme to a
  set of vertices over a single
  independent variable u.
docstr_tok: ["Apply","this","color","scheme","to","a","set","of","vertices","over","a","single","independent","variable","u","."]
code: def apply_to_curve(self, verts, u_set, set_len=None, inc_pos=None):
      """
      Apply this color scheme to a
      set of vertices over a single
      independent variable u.
      """
      bounds = create_bounds()
      cverts = []
      if callable(set_len):
          set_len(len(u_set) * 2)
      # calculate f() = r,g,b for each vert
      # and find the min and max for r,g,b
      for _u in range(len(u_set)):
          if verts[_u] is None:
              cverts.append(None)
          else:
              x, y, z = verts[_u]
              u, v = u_set[_u], None
              c = self(x, y, z, u, v)
              if c is not None:
                  c = list(c)
                  update_bounds(bounds, c)
              cverts.append(c)
          if callable(inc_pos):
              inc_pos()
      # scale and apply gradient
      for _u in range(len(u_set)):
          if cverts[_u] is not None:
              for _c in range(3):
                  # scale from [f_min, f_max] to [0,1]
                  cverts[_u][_c] = rinterpolate(
                      bounds[_c][0], bounds[_c][1], cverts[_u][_c]
                  )
              # apply gradient
              cverts[_u] = self.gradient(*cverts[_u])
          if callable(inc_pos):
              inc_pos()
      return cverts
  
imports: from sympy.core.basic import Basic
  from sympy.core.symbol import Symbol, symbols
  from sympy.utilities.lambdify import lambdify
  from .util import interpolate, rinterpolate, create_bounds, update_bounds
  from sympy.utilities.iterables import sift
label_desc: Use image node_id 8 for calling the ColorScheme obj's underlying member method code with example usage: obj.apply_to_curve(verts, u_set, set_len, inc_pos) and returns: cverts