Lower semicontinuity (source code)

= Lower semicontinuity

= Lower semicontinuous
{synonym}

A function is lower semicontinuous when its strict superlevel sets are open, equivalently when its sublevel sets are closed. In Euclidean spaces this is the <sequential lower semicontinuity> condition $f(x)\leq\liminf_k f(x_k)$ whenever $x_k\to x$. This closedness property is essential to existence of proximal minimizers.