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2 Complexes
 2.1 Categories and filters
 2.2 Creating chain and cochain complexes
 2.3 Attributes
 2.4 Operations
 2.5 Truncations

2 Complexes

2.1 Categories and filters

2.1-1 IsChainOrCochainComplex
‣ IsChainOrCochainComplex( C )( filter )
‣ IsChainComplex( C )( filter )
‣ IsCochainComplex( C )( filter )
‣ IsBoundedBelowChainOrCochainComplex( C )( filter )
‣ IsBoundedAboveChainOrCochainComplex( C )( filter )
‣ IsBoundedChainOrCochainComplex( C )( filter )
‣ IsBoundedBelowChainComplex( C )( filter )
‣ IsBoundedAboveChainComplex( C )( filter )
‣ IsBoundedChainComplex( C )( filter )
‣ IsBoundedBelowCochainComplex( C )( filter )
‣ IsBoundedAboveCochainComplex( C )( filter )
‣ IsBoundedCochainComplex( C )( filter )

Returns: true or false

Gap-categories for chain and cochain complexes.

2.2 Creating chain and cochain complexes

2.2-1 ChainComplex
‣ ChainComplex( A, diffs )( operation )
‣ CochainComplex( A, diffs )( operation )

Returns: a chain complex

The input is category A and a \mathbb{Z}-function diffs. The output is the chain (resp. cochain) complex M_{\bullet}\in \mathrm{Ch}(A) (M^{\bullet}\in \mathrm{Ch}^\bullet(A)) where d^M_{i}=\mathrm{diffs}[ i ](d_M^{i}=\mathrm{diffs}[ i ]).

2.2-2 ChainComplex
‣ ChainComplex( diffs, n )( operation )
‣ CochainComplex( diffs, n )( operation )

Returns: a (co)chain complex

The input is a finite dense list diffs and an integer n . The output is the chain (resp. cochain) complex M_{\bullet}\in \mathrm{Ch}(A) (M^{\bullet}\in \mathrm{Ch}^\bullet(A)) where d^M_{n}:= \mathrm{diffs}[ 1 ](d_M^n :=\mathrm{diffs}[ 1 ]),d^M_{n+1}=\mathrm{diffs}[ 2 ](d_M^{n+1}:=\mathrm{diffs}[ 2 ]), etc.

2.2-3 ChainComplex
‣ ChainComplex( diffs )( operation )
‣ CochainComplex( diffs )( operation )

Returns: a (co)chain complex

The same as the previous operations but with n=0.

2.2-4 StalkChainComplex
‣ StalkChainComplex( M, n )( operation )
‣ StalkCochainComplex( M, n )( operation )

Returns: a (co)chain complex

The input is an object M\in A. The output is chain (resp. cochain) complex M_{\bullet}\in\mathrm{Ch}_\bullet(A)(M^{\bullet}\in\mathrm{Ch}^\bullet(A)) where M_n=M( M^n=M) and M_i=0(M^i=0) whenever i\neq n.

2.2-5 ChainComplexWithInductiveSides
‣ ChainComplexWithInductiveSides( d, G, F )( operation )

Returns: a chain complex

The input is a morphism d\in A and two functions F,G. The output is chain complex M_{\bullet}\in\mathrm{Ch}_\bullet(A) where d^{M}_{0}=d and d^M_{i}=G^{i}(d) for all i\leq -1 and d^M_{i}=F^{i}(d ) for all i \geq 1.

2.2-6 ChainComplexWithInductiveSides
‣ ChainComplexWithInductiveSides( n, d, G, F )( operation )

Returns: a chain complex

The input is an integer n, a morphism d\in A and two functions F,G. The output is chain complex M_{\bullet}\in\mathrm{Ch}_\bullet(A) where d^{M}_{n}=d and d^M_{i}=G^{i}(d) for all i\leq -1 and d^M_{i}=F^{i}(d ) for all i \geq 1.

2.2-7 CochainComplexWithInductiveSides
‣ CochainComplexWithInductiveSides( d, G, F )( operation )

Returns: a cochain complex

The input is a morphism d\in A and two functions F,G. The output is cochain complex M^{\bullet}\in\mathrm{Ch}^\bullet(A) where d_{M}^{0}=d and d_M^{i}=G^{i}( d) for all i\leq -1 and d_M^{i}=F^{i}( d ) for all i \geq 1.

2.2-8 ChainComplexWithInductiveNegativeSide
‣ ChainComplexWithInductiveNegativeSide( d, G )( operation )

Returns: a chain complex

The input is a morphism d\in A and a functions G. The output is chain complex M_{\bullet}\in\mathrm{Ch}_\bullet(A) where d^{M}_{0}=d and d^M_{i}=G^{i}( d ) for all i\leq -1 and d^M_{i}=0 for all i \geq 1.

2.2-9 ChainComplexWithInductivePositiveSide
‣ ChainComplexWithInductivePositiveSide( d, F )( operation )

Returns: a chain complex

The input is a morphism d\in A and a functions F. The output is chain complex M_{\bullet}\in\mathrm{Ch}_\bullet(A) where d^{M}_{0}=d and d^M_{i}=F^{i}( d ) for all i\geq 1 and d^M_{i}=0 for all i \leq 1.

2.2-10 CochainComplexWithInductiveNegativeSide
‣ CochainComplexWithInductiveNegativeSide( d, G )( operation )

Returns: a cochain complex

The input is a morphism d\in A and a functions G. The output is cochain complex M^{\bullet}\in\mathrm{Ch}^\bullet(A) where d_{M}^{0}=d and d_M^{i}=G^{i}( d ) for all i\leq -1 and d_M^{i}=0 for all i \geq 1.

2.2-11 CochainComplexWithInductivePositiveSide
‣ CochainComplexWithInductivePositiveSide( d, F )( operation )

Returns: a cochain complex

The input is a morphism d\in A and a functions F. The output is cochain complex M^{\bullet}\in\mathrm{Ch}^\bullet(A) where d_{M}^{0}=d and d_M^{i}=F^{i}( d ) for all i\geq 1 and d_M^{i}=0 for all i \leq 1.

2.3 Attributes

2.3-1 Differentials
‣ Differentials( C )( attribute )

Returns: a \mathbb{Z}-function

The command returns the differentials of the chain or cochain complex as a \mathbb{Z}-function.

2.3-2 Objects
‣ Objects( C )( attribute )

Returns: a \mathbb{Z}-function

The command returns the objects of the chain or cochain complex as a \mathbb{Z}-function.

2.3-3 AsChainComplex
‣ AsChainComplex( C )( attribute )

Returns: a chain complex

If the input is a cochain complex C, then the output is the associated chain complex. Otherwise, the output is C.

2.3-4 AsCochainComplex
‣ AsCochainComplex( C )( attribute )

Returns: a cochain complex

If the input is a chain complex C, then the output is the associated cochain complex. Otherwise, the output is C.

2.3-5 IsExact
‣ IsExact( C )( property )

Returns: a boolian

The input is a bounded chain (resp. cochain) complex C and two integers m,n. The output is true when C is an exact complex, otherwise the output is false.

2.3-6 IsContractable
‣ IsContractable( C )( property )

Returns: a boolian

The input is a bounded chain (resp. cochain) complex C and two integers m,n. The output is true when C is a contractible complex, otherwise the output is false.

2.4 Operations

2.4-1 \[\]
\[\]( C, i )( operation )

Returns: an object

The command returns the object of the chain or cochain complex in index i.

2.4-2 \^
‣ \^( C, i )( operation )

Returns: a morphism

The command returns the differential of the chain or cochain complex in index i.

2.4-3 CyclesAt
‣ CyclesAt( C, n )( operation )

Returns: a morphism

The input is a chain or cochain complex C and an integer n. The output is the kernel embedding of the differential in index n.

2.4-4 BoundariesAt
‣ BoundariesAt( C, n )( operation )

Returns: a morphism

The input is a chain (resp. cochain) complex C and an integer n. The output is the image embeddin of i+1'th ( resp. i-1'th) differential of C.

2.4-5 GeneralizedEmbeddingOfHomologyAt
‣ GeneralizedEmbeddingOfHomologyAt( C, n )( operation )

Returns: a generalized morphism

The input is a chain complex and an integer n. The output is the generalized embedding (defined by span) of the homology object at index n.

2.4-6 GeneralizedProjectionOntoHomologyAt
‣ GeneralizedProjectionOntoHomologyAt( C, n )( operation )

Returns: a generalized morphism

The input is a chain complex and an integer n. The output is the generalized embedding (defined by span) on the homology object at index n.

2.4-7 GeneralizedEmbeddingOfCohomologyAt
‣ GeneralizedEmbeddingOfCohomologyAt( C, n )( operation )

Returns: a generalized morphism

The input is a chain complex and an integer n. The output is the generalized embedding (defined by span) of the cohomology object at index n.

2.4-8 GeneralizedProjectionOntoCohomologyAt
‣ GeneralizedProjectionOntoCohomologyAt( C, n )( operation )

Returns: a generalized morphism

The input is a chain complex and an integer n. The output is the generalized projection (defined by span) on the cohomology object at index n.

2.4-9 DefectOfExactnessAt
‣ DefectOfExactnessAt( C, n )( operation )
‣ CohomologyAt( C, n )( operation )
‣ HomologyAt( C, n )( operation )

Returns: an object

The input is a chain (resp. cochain) complex C and an integer n. The outout is the homology (resp. cohomology) object of C at index n. The input is a (co)chain complex C and an integer n. The outout is the (co)homology object of C at index n.

2.4-10 HomologySupport
‣ HomologySupport( C, m, n )( operation )
‣ CohomologySupport( C, m, n )( operation )

Returns: a list

The input is a chain (resp. cochain) complex C and two integers m,n. The outout is the list of indices where the homology (resp. cohomology) objects of C are not zero.

2.4-11 HomologySupport
‣ HomologySupport( C )( operation )
‣ CohomologySupport( C )( operation )

Returns: a list

The same as above but for bounded complexes.

2.4-12 ObjectsSupport
‣ ObjectsSupport( C, m, n )( operation )
‣ DifferentialsSupport( C, m, n )( operation )

Returns: a list

The input is a chain (resp. cochain) complex C and two integers m,n. The outout is the list of indices where the objects (resp. differentials) of C are not zero.

2.4-13 ObjectsSupport
‣ ObjectsSupport( C )( operation )
‣ DifferentialsSupport( C )( operation )

Returns: a list

The same as above but for bounded complexes.

2.4-14 AsComplexOverCapFullSubcategory
‣ AsComplexOverCapFullSubcategory( A, C )( operation )

Returns: an object

The input is a full subcategory A of some category B and a complex C in \mathrm{Ch}(B), where all objects of C actually lie in A. The output is C considered in \mathrm{Ch}(A).

2.4-15 IsWellDefined
‣ IsWellDefined( C, m, n )( operation )

Returns: true or false

The input is a chain (resp. cochain) complex C and two integers m,n. The output is true when C is well defined in the interval [m,\dots,n] and false otherwise.

2.4-16 IsWellDefined
‣ IsWellDefined( arg )( property )

Returns: true or false

2.4-17 IsExactInIndex
‣ IsExactInIndex( C, n )( operation )

Returns: true or false

The input is a chain or cochain complex C and an integer n. The outout is true if C is exact in i. Otherwise the output is false.

2.4-18 SetUpperBound
‣ SetUpperBound( C, n )( operation )

Returns: Side effect

The command sets an upper bound n to the chain (resp. cochain) complex C. This means C_{i}=0(C^{i}=0) for i>n. This upper bound will be called \textit{active} upper bound of C. If C already has an active upper bound m, then m will be replaced by n only if n is better upper bound than m, i.e., m>n.

2.4-19 SetLowerBound
‣ SetLowerBound( C, n )( operation )

Returns: Side effect

The command sets an lower bound n to the chain (resp. cochain) complex C. This means C_{i}=0(C^{i}=0) for n>i. This lower bound will be called \textit{active} lower bound of C. If C already has an active lower bound m, then m will be replaced by n only if n is better lower bound than m, i.e., n>m.

2.4-20 HasActiveUpperBound
‣ HasActiveUpperBound( C )( operation )

Returns: true or false

The input is chain or cochain complex. The output is true if an upper bound has been set to C and false otherwise.

2.4-21 HasActiveLowerBound
‣ HasActiveLowerBound( C )( operation )

Returns: true or false

The input is chain or cochain complex. The output is true if a lower bound has been set to C and false otherwise.

2.4-22 ActiveUpperBound
‣ ActiveUpperBound( C )( operation )

Returns: an integer

The input is chain or cochain complex. The output is its active upper bound if such has been set to C. Otherwise we get error.

2.4-23 ActiveLowerBound
‣ ActiveLowerBound( C )( operation )

Returns: an integer

The input is chain or cochain complex. The output is its active lower bound if such has been set to C. Otherwise we get error.

2.4-24 DisplayComplex
‣ DisplayComplex( C, m, n )( operation )

Returns: nothing

The input is chain or cochain complex C and two integers m and n. The command displays all components of C between the indices m,n.

2.4-25 ViewComplex
‣ ViewComplex( C, m, n )( operation )

Returns: nothing

The input is chain or cochain complex C and two integers m and n. The command views all components of C between the indices m,n.

2.5 Truncations

2.5-1 GoodTruncationBelow
‣ GoodTruncationBelow( C, n )( operation )

Returns: chain complex

2.5-2 GoodTruncationAbove
‣ GoodTruncationAbove( C, n )( operation )

Returns: chain complex

2.5-3 GoodTruncationAbove
‣ GoodTruncationAbove( C, n )( operation )

2.5-4 GoodTruncationBelow
‣ GoodTruncationBelow( C, n )( operation )

Returns: cochain complex

2.5-5 BrutalTruncationBelow
‣ BrutalTruncationBelow( C, n )( operation )

Returns: chain complex

2.5-6 BrutalTruncationAbove
‣ BrutalTruncationAbove( C, n )( operation )

Returns: chain complex

2.5-7 BrutalTruncationAbove
‣ BrutalTruncationAbove( C, n )( operation )

Returns: chain complex

2.5-8 BrutalTruncationBelow
‣ BrutalTruncationBelow( C, n )( operation )

Returns: chain complex

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