2.1 Extended Real-Valued Functions and Closedness
- real-valued function: can take any real value without null value and
- extended real-valued function:can take any real value, as well as
- domain: ex2.1 . then
- epigraph of f: [f is closed if epi(f) is closed]
- lower semicontinuity:
- level set:
Note :f is lower semicontinuous<=>f is closed<=>