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TSparseMtx.TripletsToSparse Method (integer, integer, TIntegerArray, TIntegerArray, TDoubleArray, double, boolean)
TSparseMtx Class | TSparseMtx Members | Sparse Namespace | TripletsToSparse Method | Example | See Also
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Convert triplets to sparse format.

Pascal
procedure TripletsToSparse(RowCount: integer; ColCount: integer; const SrcRow: TIntegerArray; const SrcColumn: TIntegerArray; const SrcValues: TDoubleArray; Threshold: double = 0; PreserveZeroDiagElem: boolean = true); overload;
Description

A sparse matrix can also be presented as pairs of the three elements called triplets. For each non zero value in the matrix we specify it's position: Row, Column, and it's Value. MatrixSize defines the size of the matrix and sets the Size and Cols properties. The maximum row and column index may not exceed rowCount and colCount. This is usually the most efficient way to convert a given dense matrix to sparse format. The values do not need to be ordered, the same coordinates can appear more than once. All values having the same coordinates will be summed together. This routine can therefore also be used as a way to sum multiple sparse matrices. Triplets can be represented by three arrays: Row, Column and Values or they can all be stored in one TMtx matrix. 

By default any zeros on the main diagonal will be preserved. Set the last parameter to false to drop them on conversion.

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Example

Test sparseToTriplets, TripletsToSparse methods.

var R1,C1: TIntArray; V1: TDoubleArray; SparseA, SparseB: TSparseMtx; A: Matrix; begin SparseA := TSparseMtx.Create; SparseB := TSparseMtx.Create; try // setup sparse , rows, cols, non-zero elements SetLength(R1,SparseA.NonZeros); SetLength(C1,SparseA.NonZeros); SetLength(V1,SparseA.NonZeros); SparseA.SparseToTriplets(R1,C1,V1); SparseB.TripletsToSparse(SparseA.Cols,SparseA.Cols,R1,C1,V1); SparseA.SparseToDense(A); if not SparseB.Equal(SparseA,1E-5) then ERaise('Not equal'); if not SparseA.Equal(A,0,True) then ERaise('Not equal'); SparseA.SparseToTriplets(A); SparseB.TripletsToSparse(SparseA.Cols,SparseA.Cols,A); if not SparseA.Equal(SparseB) then ERaise('Not equal'); finally SparseA.Free; SparseB.Free; end; end;
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