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Circles applet 
InstructionsTwo sliders are used to change the pattern parameters
ExplanationThe pattern is based on a square array of coordinates with (0,0) being in the centre. For each square the value of
z = k * (x * x + y * y)
is calculated. The Fractional part of 'z' is calculated (z  int (z)) and mapped onto a colour. It the screen had infinite resolution this would create a pattern of concentric circular bands, getting progressively narrower as they get further from the centre. Sampling this pattern with the discrete points on our square grid creates this applet's more complicated displays. 


(c) John Whitehouse 2011
