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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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