Function Description
********************

	Name: CRYSTAL 
	Function: f(x) = a0 + a1*cos(2x) + a2*sin(2x)
	Parameters: a0 a1 a2

Notes
*****

	Single crystal fit function as suggested by Gump Zhao.
	

C-code for the function
***********************

	answer = a[0] + a[1]*cos(2*x) + a[2]*sin(2*x);