NumberQ[expr] gives True if expr is a number, and False otherwise.

Ordering[list] gives the positions in list at which each successive element of Sort[list] appears. Ordering[list, n] gives the positions in list at which the first n elements ...

RandomComplex[] gives a pseudorandom complex number with real and imaginary parts in the range 0 to 1.RandomComplex[{z_min, z_max}] gives a pseudorandom complex number in the ...

Read[stream] reads one expression from an input stream and returns the expression. Read[stream, type] reads one object of the specified type. Read[stream, {type_1, type_2, ...

RealExponent[x] gives log_10 (|x|).RealExponent[x, b] gives log_b (|x|).

Real is the head used for real (floating-point) numbers.

ReflectionTransform[v] gives a TransformationFunction that represents a reflection in a mirror through the origin, normal to the vector v.ReflectionTransform[v, p] gives a ...

SetAccuracy[expr, a] yields a version of expr in which all numbers have been set to have accuracy a.

Sow[e] specifies that e should be collected by the nearest enclosing Reap. Sow[e, tag] specifies that e should be collected by the nearest enclosing Reap whose pattern ...

TableSpacing is an option for TableForm and MatrixForm which specifies how many spaces should be left between each successive row or column.