A cubic-interpolating sound generator based on a function given in Clifford Pickover's book Chaos In Wonderland, pg 26. The function is:
    x(n+1) = sin(b * y(n)) + c * sin(b * x(n))
    y(n+1) = sin(a * x(n)) + d * sin(a * y(n))
According to Pickover, parameters a and b should be in the range from -3 to +3, and parameters c and d should be in the range from 0.5 to 1.5. The function can, depending on the parameters given, give continuous chaotic output, converge to a single value (silence) or oscillate in a cycle (tone).
sclang code translation:
| freq | 
 Iteration frequency in Hertz  | 
| a | 
 Equation variable  | 
| b | 
 Equation variable  | 
| c | 
 Equation variable  | 
| d | 
 Equation variable  | 
| xi | 
 Initial value of x  | 
| yi | 
 Initial value of y  |