= Scalar-valued function
{title2=$f:X\to\mathbb F$}
A <scalar-valued function> is a <function> whose <codomain> is a <field>, typically the <real numbers> or <complex numbers>. Its output is a single <scalar>, while its input can belong to an arbitrary <set>. For example, the square of the <norm> of a <vector> is real-valued. In a relativistic application, being scalar-valued alone does not establish <Lorentz invariance>: the transformation of the input and of the complete quantity must also be specified.
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