title: How to fit a quadratic model knowing the maximum in R?
body: <p>I have a data frame x and y, and I know the maximum of y. I want to fit this data to a quadratic model. How can I do it in R knowing the maximum? If I didn't know the maximum, I would fit it with lm(y~x + I(x^2)). Can anyone has an idea about this? Thanks in advance!</p>