No, you're missing my point. Yes, you can use those formulas to dscribe the circle. However, you can only draw a finite number of points, because your computer screen has a finite number of pixels. In this way, the circle that is drawn is not continuous. The circle is drawn imperfectly. To draw it perfectly would require you draw all, infinite points, described by that equation x^2 + y^2 = r^2. The circle drawn on your screen is "discrete" in nature ( a finite number of points. ) This is its inefficiency. Its imperfect.
You seem very late to the party. While no one has complete stats on this, evidence strongly indicates that algorithmic trading, especially the very short-term variety, peaked in the 2008-9 period and has been shrinking, both in profitability and headcount, since. A steady flow of HFT shops are now selling out at a discount or outright closing shop. http://www.advancedtrading.com/as-hft-profits-slump-the-hot-trend-loses/240009067