What to do when you want to research something your advisor does not want you to? When entering my MS I had an advisor assigned to me because I didn't finish undergrad in the university I'm now in. I want to research graph theory but my advisor researches in computational geometry, and every problem I proposed to him he dismissed as being too difficult (without really explaining why) and proposed an optimization problem with metaheuristics instead. As I'm approaching the end of the first semester now, I need to have an advisor confirmed and a topic semi-defined, so I half-heartedly accepted one of the problems he proposed just to get on with it. 

Now it is about 3 days later and I'm already regretting the decision I made: I'm 22 years old and really like researching, but the thought of dedicating 2 years of my life on something I'm "meh" about does not make me happy. I think it is clear my advisor isn't going to open his mind to new ideas but is it too late to switch advisors? Since dropping out is not an option, as I moved from a different city and just settled in here, what should I do about it? Should I give up convincing him and try to find a new advisor in a month? Is it "normal" for people to take a research topic they don't really like for a masters program?

Edit: I realised I made a bad choice of word that made me seem like I am mad or demanding something from my advisor. I edited my question.
This sounds like you are mad at your supervisor, however, keep in mind that researchers are often very specialized in a particular field, and would have difficulties supervising a project in a different field, or using a method they are not familiar with. THerefore, if you want to do a particular project/work in a particular field/with a particular method, it's up to YOU to find a supervisor that has the matching expertise. Otherwise, you may indeed do what your supervisor suggests you.

Where I work, students have the opportunity to choose their own supervisor that matches their interests. If they don't, they will get assigned to someone. In that case, the students are warned that they may have to do a project that is suggested by the supervisor.

Sounds like it is the same at your place. And in that case, it is normal to do something that you don't really like.

Let me tell you, it's better to work at something you do like. Therefore, get out and find a supervisor that works in your field/method. And don't blame the supervisor for having his own interests.