When math professor Ronnie Lee failed to show up for class on Oct. 1 and 3, his multi-variable calculus students became concerned about the popular professor.

The students were right to be worried, because Lee had suffered a stroke sometime before his Oct. 1 class. He has greatly improved from his initial critical condition and is preparing to enter a rehabilitation process, colleagues who visited him at Yale-New Haven Hospital said.

Professor Andrew Casson has visited Lee three times in the hospital and said Lee has looked better each visit.

“He’s been awake,” Casson said. “They say he will probably go through rehabilitation, and it will be a long process. I don’t think they’re able to say at the present to what extent he will recover.”

Since Lee lives alone, no one reported the stroke when it occurred because he was at home. The math department called the police to report his absence, and the police broke down the door and found Lee in critical condition, according to an e-mail written by math Director of Undergraduate Studies Efim Zelmanov to Deputy Dean of Yale College Joseph Gordon and Mac Caplan ’05, a student in Lee’s Math 120 class.

Zelmanov said in the e-mail that students in Lee’s Math 120 class could join another section taught at the same time.

Math professor Richard Beals also visited Lee and said he was conscious but unable to speak last week.

“The hospital was talking in terms of speech and physical therapy,” Beals said. “[But] he’s definitely conscious. I’m sure he was aware of his surroundings.”

Although students in Lee’s classes have joined other sections, they said they would miss Lee’s charm.

“Honestly, I’ve never seen anyone who had a more permanent smile on his face,” Alex Levitt ’05 said. “He was always genuinely happy. He always had chalk on his hands because he never used an eraser.”

Lisa Holme ’05 said Lee tried to share his enthusiasm for math with his students.

“I really liked that he would get excited about stuff like he was about to show us something really cool,” Holme said.