[R] force glm estimates to be nonnegative

[Michele Christina Itten]

Is there a way to force certain formula parameters to be nonnegative?

What I want to do is to estimate student capacity over time, namely by

>  capacity ~ Student + Student:Day

I add this formula to a glm call and obtain negative learning slope estimates (Student:Day) in some cases. 
However, I don't want to allow for that. In such a case, glm should solve 

> capacity ~ Student

and I will set the slope to zero. 

Is there an option to constrain a parameter set to nonnegative values?




Many thanks in advance!

Michele Itten,
BS. Carnegie Mellon