What function or operation am I looking for?

[minio]

First, I am sorry for very unspecific topic, but I really have no clue what I am looking for. I need some way how in mathematical terms describe things like following:
I have line segment of length l and I have sine function with period length \lambda originating at one end of line segment. If l=\lambda I can easily count that there will be three points on the segment where sine value will be 0. But If \lambda is slightly shorter there still will be three such points until l=\frac{3}{2}\lambda. Then there will be four of them. How can I describe number of such points as f(l,\lambda)?
What should I look for/study? Frankly I wouldn't be surprised if it is something really basic, because I tend to miss basic things :/ Thank you in advance

 

[dodo]

So, you want to know how many zeroes are in a sine wave l/\lambda periods long. Which should be \lfloor 2l/\lambda \rfloor+1 zeroes in total, where the brackets represent the floor function.

 

[minio]

Thank you. I never heard of floor function before. Now it is clear, that in general I was looking for floor/ceiling functions.

 

[dodo]

You're welcome!

If the ratio 2l/\lambda is positive (as it will presumably be in your case), then \lfloor 2l/\lambda \rfloor is simply the integer part of that ratio. For example, if 2l/\lambda was 17.936, then \lfloor 2l/\lambda \rfloor would be just 17.