“…During classification, some popular techniques to optimize the feature distances of hard classes are summarized. [17,20,24,28,31,34,36,38,39,58,61,63,65,67,68,70,72,74,76,77,81,[89][90][91][92]96,106,109,115,119,124,126,128,131,[145][146][147][148]150,152,155,159,164,165,169,176,187,189,190,197,200,…”