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documentation:ref:simpletensor [2015/11/21 12:33] (current)
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 +====== SimpleTensor ======
 +''​SimpleTensor''​ represents a simple tensors like ''​f_mn''​ of symbols like ''​x''​ etc. Like any other expression, it inherits all properties of [[Tensor]]. ''​SimpleTensor''​ adopts the following convention on its indices: the indices of ''​SimpleTensor''​ ([[SimpleIndices]]) are sorted by their [[documentation:​ref:​IndexType|types]],​ but the relative ordering of indices within a particular type is same as defined by the user:
 +<sxh groovy; gutter: false>
 +def t = '​f_cba^\\alpha_AB'​.t
 +println t.indices
 +<sxh plain; gutter: false>
 +   > _{cbaAB}^{\alpha}
 +The relative ordering is not changed even if tensor has [[documentation:​guide:​symmetries_of_tensors|symmetry property]]; in latter case Redberry uses algorithms provided by [[documentation:​guide:​mappings_of_indices]] to compare expressions instead of trying to put expression in canonical form.
 +The distinctive feature of simple tensors is the presence of [[documentation:​guide:​symmetries_of_tensors|symmetries]]. In order to bind symmetries to simple tensor, one can use ''​addSymmetry''​ method or directly call ''​addSymmetry''​ from simple tensor [[SimpleIndices]]:​
 +<sxh groovy; gutter: false>
 +addSymmetry '​f_pqr',​ [1, 0].p
 +//or equivalently
 +'​f_klm'​.t.indices.symmetries.addSymmetry( [1, 0].p )
 +Once specified, symmetries will be automatically set up for all same simple tensors ​ (''​f_abc''​ or ''​f_qrs''​ etc.) whichever way they are created.
 +In order to get name of simple tensor one can get ''​.stringName''​ property:
 +<sxh groovy: gutter: false>
 +def t = '​f_abc^\\alpha_AB'​.t
 +println t.stringName
 +<sxh plain; gutter: false>
 +   > f
 +On the other hand, this name does not reflect the mathematical nature of simple tensors, and for example two completely different tensors ''​f_a''​ and ''​f_ab''​ have same ''​stringName''​. ​
 +The unique identifier of ''​SimpleTensor''​ which encodes its mathematical nature is an integer property ''​.name'':​ two simple tensors have same  ''​.name''​ if and only if they have same ''​.stringName''​ and same //structure of indices//:
 +<sxh groovy: gutter: false>
 +assert '​f_ab'​.t.name == '​f_bc'​.t.name
 +assert '​f_ab'​.t.name != '​t_bc'​.t.name
 +assert '​f_ab'​.t.name != '​f_b'​.t.name
 +assert '​f_ab'​.t.name != '​f_AB'​.t.name
 +For further details see API.
 +====See also====
 +  * Related guides: [[documentation:​guide:​tensors_and_indices]],​ [[documentation:​guide:​symmetries_of_tensors]]
 +  * Reference: [[documentation:​ref:​tensor]], ​ [[documentation:​ref:​simpleindices]], ​ [[documentation:​ref:​tensorfield]]
 +  * JavaDocs: [[http://​api.redberry.cc/​redberry/​1.1.9/​java-api/​cc/​redberry/​core/​tensor/​SimpleTensor.html| SimpleTensor]]
 +  * Source code: [[https://​bitbucket.org/​redberry/​redberry/​src/​tip/​core/​src/​main/​java/​cc/​redberry/​core/​tensor/​SimpleTensor.java|SimpleTensor.java]]