Compute isomorphism between two graphs

computes a graph isomorphism
equivalence relation between graphs `P`

= isomorphism(`G1,G2`

)`G1`

and `G2`

,
if one exists. If no isomorphism exists, then `P`

is an empty
array.

specifies additional options with one or more name-value pair arguments. For
example, you can specify `P`

= isomorphism(___,`Name,Value`

)`'NodeVariables'`

and a list of node
variables to indicate that the isomorphism must preserve these variables to be
valid.