<human>:  Why did the author choose to write about Srinivasa Ramanujan in the book ‘The Man Who Knew Infinity’?
<bot>: The author chose to write about Srinivasa Ramanujan because he was an interesting mathematician. He had an amazing mathematical mind and was very passionate about mathematics. Ramanujan was a self-taught mathematician, and he was only 20 years old when he wrote his first paper on mathematics. He was also a very humble person who never thought of himself as being very smart. He was very interested in the number pi, and spent most of his time studying and thinking about it. Ramanujan also made some very important contributions to the field of mathematics.