### astMapSplit

Split a Mapping up into parallel component Mappings

#### Description:

This function creates a new Mapping which connects specified inputs within a supplied Mapping to the corresponding outputs of the supplied Mapping. This is only possible if the specified inputs correspond to some subset of the Mapping outputs. That is, there must exist a subset of the Mapping outputs for which each output depends only on the selected Mapping inputs, and not on any of the inputs which have not been selected. Also, any output which is not in this subset must not depend on any of the selected inputs. If these conditions are not met by the supplied Mapping, then a NULL Mapping pointer is returned.

#### Synopsis

void astMapSplit( AstMapping $\ast$this, int nin, const int $\ast$in, int $\ast$out, AstMapping $\ast$$\ast$map )

#### Parameters:

##### this
Pointer to the Mapping to be split.
##### nin
The number of inputs to pick from " this" .
##### in
Pointer to an array holding the indices within the supplied Mapping of the inputs which are to be picked from the Mapping. This array should have " nin" elements. If " Nin" is the number of inputs of the supplied Mapping, then each element should have a value in the range 1 to Nin.
##### out
Pointer to an array in which to return the indices of the outputs of the supplied Mapping which are fed by the picked inputs. A value of one is used to refer to the first Mapping output. The supplied array should have a length at least equal to the number of outputs in the supplied Mapping. The number of values stored in the array on exit will equal the number of outputs in the returned Mapping. The i’ th element in the returned array holds the index within the supplied Mapping which corresponds to the i’ th output of the returned Mapping.
##### map
Address of a location at which to return a pointer to the returned Mapping. This Mapping will have " nin" inputs (the number of outputs may be different to " nin" ). NULL is returned if the supplied Mapping has no subset of outputs which depend only on the selected inputs. The returned Mapping is a deep copy of the required parts of the supplied Mapping.

#### Notes:

• If this function is invoked with the global error status set, or if it should fail for any reason, then a NULL value will be returned for the " map" pointer.