[R] a maximazation question

[Shuangge Ma]

Dear Sir/Madam:
this is shuangge Ma, graduate student in UW-Madison statistics department. 
I have a computational question.
I have a function f(x,y). I want to find the y(x) that maximize f(x,y)
under the constraint y(x) is a non-decreasing step function.
Is there any R package or algorithm I can use for this purpose?
thanks a lot for your time and help, 

Sincerely,
Shuangge Ma