Index

Modulated structures dictionary (msCIF) version 3.2.1

_function.Sawtooth

Definition:

   

      The function:

            s = Sawtooth(a, c, w, x4)

      returns

            2* a * ((x4-c)/w)

      for x4 belonging to the interval [c-(w/2), c+(w/2)], where a is the array
      containing the the amplitudes (maximum displacements) along each 
      crystallographic axis, w is the width of the sawtooth, x4 is a particular value 
      of the internal coordinate and c is the centre of the function in
      internal space. The use of this function is restricted to one-dimensional 
      modulated structures.     

Type: Real

Values appear in Array context.

Dimension: [3]

Evaluation method:

      Function Sawtooth( a  :[Array, Real] ,
                         c  :[Single, Real],
                         w  :[Single, Real],
                         x4 :[Single,Real] )
      {
      
        Sawtooth = [0.0,0.0,0.0]

        If ( c-w/2.0 <= x4 and x4 <= c+w/2.0 ) Sawtooth = 2*a*(x4-c)/w

      }

# Heavier alternative: only atom label and x4

      Function Sawtooth( atlab :[Single, Code],
                         x4    :[Single,Real] )
      {
# Atom not in list of sawtooth modulation or null sawtooth width      
        Sawtooth = [-1.0,-1.0,-1.0]  

        Loop d as atom_site_displace_special_func {

          If (atlab == d.atom_site_label and d.sawtooth_w != 0.0){

            Sawtooth = [0.0,0.0,0.0]

            If ( d.sawtooth_c-d.sawtooth_w/2.0 <= x4 and 
                                            x4 <= d.sawtooth_c+d.sawtooth_w/2.0 ) 
             
                     Sawtooth = 2*d.sawtooth_axyz*(x4- d.sawtooth_c)/d.sawtooth_w

            Break

          } # End of If

        }   # End of Loop

      }

Category:
function