Yoga as concentration rather than union.
"The two important features of Yoga to be noted are (i) that there is a suppression at will, of the modifications of the mind and (ii) that it is not casual but has been developed into a habit through constant practice, not for gaining a personal end, but in the spirit of renunciation". p xvii
Ramaswami recommended, Samkhya master, Swami Hariharananda Aranya's commentary on the Yoga Sutras.
Nicely laid out, very readable and smart, constant Ahhhhh factor. Have a look at the Amazon link above. The layout tends to be the Sutra and Vyasas' commentary in Sanskrit, the English translations with note indicators of both followed by Aranya's commentary.
(1869-1947) spent six years of his early monastic life in utter seclusion in the caves of Barabar Hills, Bihar, India. His possessions were the barest minimum, even for a Sannyasin. He devoted the whole time to gain the mastery over his mind, which is Yoga. Having attained his goal, he returned to the world of men. Continuing the secluded and austere lifestyle and intense spiritual practice he began disseminating the message of Samkhya-yoga through books in Bengali and Sanskrit. Emanating from his own experience it was unique, logical and penetrating Not only did he delineate the path of Yoga, he inspired and guided seekers to tread it. In April 1947, his body frail from age and years of penance started becoming a burden; he saw the signal and at once decided against continuing further. The end came peacefully, a fitting finale to a great and noble life.
This from the introduction...
googling the Author I found this about the Samkhya math he founded
Established in 1927-28 by Samkhya-yogacharya Swami Hariharananda Aranya. The founder came from an educated wealthy zamindar family in Bengal. In his student days, he felt the urge to renounce the world and don the robe of a sannyasin. In his search he met many spiritual adepts but was not fully satisfied until he chanced upon a copy of an ancient text on Samkhya-yoga in a library. It resulted in his leaving the home, taking the vow of a sannyasin and becoming a mendicant.
Acharya Swamiji passed his early monastic life (1892-1898) in the caves of Barabar hills in Bihar where his earthly resources consisted of a blanket, a thick cotton shirt, a single piece of dhoti, a napkin and a wooden kamandulu (water pot). A devout and generous villager from two miles from the cave provided Swamiji with the means of his subsistence, which was brought to him once every noon. In absence of utensils, that frugal meal was deposited on a black stone and sparkling water from nearby mountain springs satisfied his thirst. He devoted the whole time to gain mastery over his mind, which is Yoga.
Having attained his goal, he returned to the world of men. He continued the same secluded austere lifestyle and intense spiritual practice in places like Tribeni in Hoogly district in West Bengal, Varanasi, Hardwar, Rishikesh and in other places in the Himalayas and finally decided to settle down at Madhupur, Jharkhand (formerly Bihar). He had already began disseminating the message of Samkhya-yoga through books in Bengali and Sanskrit. Emanating from his own experience it was unique, logical and penetrating.
Attracted by his unique personality some genuine seekers after truth found him out in the small town of Madhupur and one of them volunteered to build a suitable house containing an artificial cave as the permanent home of the Master. Thus did Kapil Math came into existence. First a dwelling, and an artificial cave with it's one and only entrance permanently blocked, where the Master spent the rest of his life. The Math was built adjacent to the 'cave' to house his followers who responded to his call for accepting Samkhya-yoga as the only aim in their lives.
To culture Nirvana Dharma in the light of Samkhya, Yoga and cognate philosophies.
To help persons to attain spiritual advancement.
To educate and train persons in Nirvana Dharma.
To publish books on Samkhya, Yoga and cognate philosophies and to sell them or make free distribution thereof and to collect and preserve publications and manuscripts bearing on such subjects and to find and maintain a library of suitable books.
To educate and train up its monastic members and to provide them with food and shelter, if possible.
To perform acts of charity.
To diffuse philosophical and ethical knowledge.
To incorporate any institution, society or association having objects similar to those of Kapil Math, Madhupur.
To do all other such things as an incidental or conductive to attainment of the above or any of them.
Some interesting looking books here from the Kapil math