Vector spaces may not be equipped with an inner product (for instance this question). Mathematically, one can study such spaces in its own right, but I was just wondering: is there a scientific application to such spaces? For instance I will try to imagine a physical system that can be described with a vector space without an inner product but I can't come up with an easy example.
My guess is that maybe for some stochastic equations describing a system this could be achieved, but I'm not sure. I appreciate if example in Physics could be provided, but other fields (e.g. Computer Science) are welcome.