Semicomputable function
（重定向自Semicomputable）
In computability theory, a semicomputable function is a partial function ![f : \mathbb{Q} \rightarrow \mathbb{R}](/Images/godic/202502/10/d85a3b38b7a9211b3fcb85440a6fcfff5820.png")
that can be approximated either from above or from below by a computable function.
More precisely a partial function is upper semicomputable, meaning it can be approximated from above, if there exists a computable function ![\phi(x,k) : \mathbb{Q} \times \mathbb{N} \rightarrow \mathbb{Q}](/Images/godic/202502/10/99b42c38d87dba040e773f225f9255865820.png")
, where ![x](/Images/godic/202502/10/9dd4e461268c8034f5c8564e155c67a65820.png")
is the desired parameter for ![f(x)](/Images/godic/202502/10/50bbd36e1fd2333108437a2ca378be625820.png")
and ![k](/Images/godic/202502/10/8ce4b16b22b58894aa86c421e8759df35820.png")
is the level of approximation, such that: