How to request source code? During literature review for my research proposal, I have come across a professor who has published several papers in my field, some closely related to the topic of my own research. In a series of papers he uses a specific model, expanding on and extending it in each paper. In my work, I want to use the same kind of model (evolutionary) and I would love to see the source code, both to better understand and replicate the results and because it would tremendously help me in getting started. Unfortunately, I could not find it anywhere and it is not published with any of the papers.

I am wondering if and how I should ask for the code and have three related questions:


Is it common to just email and ask for the source code or would that be considered somehow inappropriate? I might well end up applying to the university that professor is teaching at, so I don't want to leave a bad impression.
Who is the appropriate person to contact? All of the papers on the model have been published by by the professor and the same two co-authors, some with additional co-authors. Should I email the professor himself, one of the co-authors, or all of them?
How much detail about my own research should I include in my email? Just what's sufficient to justify the request or more, possibly a draft of the proposal?
Whether common or not, it is acceptable to ask. Ask the main professor, who may pass on the request to a co-author. 

I'd suggest that you only give a small amount of detail in the initial request but offer to say more if you like. But don't flood the professor in the initial request. Mention that you have a draft, but don't send it. And you can certainly mention that you are interested in applying to the university. 

What happens next depends on the nature of the reply. Perhaps they will want to help you, but other outcomes are possible.