The ceremony on Tuesday was on Class Day for seniors at Columbia College. The universitywide commencement is Wednesday, but Ms. Sulkowicz said on Tuesday that she was done with her project.

As for what will become of the mattress, which she bought online, she said she would hang onto it.

“If some sort of museum wants to buy it, then I’m open to that,” she said, “but I’m not going to just throw it away.”

Mr. Nungesser, who walked briskly away from campus immediately after the ceremony, declined to comment.

The university had actively discouraged Ms. Sulkowicz from carrying the mattress. In an email sent to students on Monday, the university asked students not to bring “large objects which could interfere with the proceedings or create discomfort to others in close, crowded spaces shared by thousands of people” into the ceremonial area.

Ms. Sulkowicz said that as students were lined up before the ceremony in Alfred Lerner Hall, a woman approached her and asked her to put the mattress in a room in the hall for the duration of the ceremony. Ms. Sulkowicz, who had stated she would not walk in the ceremony if she could not carry the mattress, refused.

Later, as Ms. Sulkowicz and her friends approached the stage, the woman reappeared and again asked her not to take it onstage, saying it would “block the flow of traffic.”

Even the dean who was reading out the names seemed to get nervous, stumbling over hers.

As Ms. Sulkowicz and her friends ascended the stage, Mr. Bollinger, who had been shaking the students’ hands, turned his back and leaned down as though to pick something up from his seat. Ms. Sulkowicz leaned over the mattress, trying to catch his eye, then straightened up and kept walking, shrugging with her free hand.