## changeslist_of_most_recent_changesChanges Introduced in V8.2

The following describes the most significant changes which occurred in the AST library between versions V8.1.0 and V8.2.0:

1. A new class of MappingMapping called UnitNormMapUnitNormMap has been added that converts a vector to a unit vector relative to a specified centre, plus length. A UnitNormMap has N inputs and N+1 outputs.The lower N output coordinates represent a unit vector parallel to the supplied input vector, and the (N+1)'th output coordinate is the length of the input vector.

2. The restriction that Mappings are immutable has been extended to all Mapping classes. This means that attributes representing parameters of a Mapping's forward or inverse transformation cannot be changed after the Mapping has been created. In order to minimise the risk to existing software, this rule does not apply to Mappings that have not yet been included in other objects such as CmpMaps or FrameSets, or which have not yet been cloned. In other words, an error is reported if an attempt is made to change the nature of a Mapping's transformation, but only if the reference count of the Mapping is greater than one. The Mapping classes affected include: GrismMapGrismMap, LutMapLutMap, PcdMapPcdMap, SphMapSphMap, WcsMapWcsMap and ZoomMapZoomMap.