code: public static boolean[] getNoneZeroIdx(float[] c) {
  		boolean[] b = new boolean[c.length];
  		for (int i = 0; i < c.length; i++) {
  			if (c[i] != 0.0)
  				b[i] = true;
  		}
  		return b;
  	}
docs: 统计非零元素
  
  @param c
  @return 非零元素标记