flags
[Core module]

Variables

const unsigned int ActualPacketAccessBit
const unsigned int AlignedBit
const unsigned int DirectAccessBit
const unsigned int EvalBeforeAssigningBit
const unsigned int EvalBeforeNestingBit
const unsigned int LinearAccessBit
const unsigned int LowerTriangularBit
const unsigned int PacketAccessBit
const unsigned int RowMajorBit
const unsigned int SelfAdjointBit
const unsigned int SparseBit
const unsigned int UnitDiagBit
const unsigned int UpperTriangularBit
const unsigned int ZeroDiagBit

Detailed Description

These are the possible bits which can be OR'ed to constitute the flags of a matrix or expression.

It is important to note that these flags are a purely compile-time notion. They are a compile-time property of an expression type, implemented as enum's. They are not stored in memory at runtime, and they do not incur any runtime overhead.

See also:
MatrixBase::Flags

Variable Documentation

const unsigned int ActualPacketAccessBit

If vectorization is enabled (EIGEN_VECTORIZE is defined) this constant is set to the value PacketAccessBit.

If vectorization is not enabled (EIGEN_VECTORIZE is not defined) this constant is set to the value 0.

const unsigned int AlignedBit

means the first coefficient packet is guaranteed to be aligned

const unsigned int DirectAccessBit

Means that the underlying array of coefficients can be directly accessed. This means two things. First, references to the coefficients must be available through coeffRef(int, int). This rules out read-only expressions whose coefficients are computed on demand by coeff(int, int). Second, the memory layout of the array of coefficients must be exactly the natural one suggested by rows(), cols(), stride(), and the RowMajorBit. This rules out expressions such as DiagonalCoeffs, whose coefficients, though referencable, do not have such a regular memory layout.

const unsigned int EvalBeforeAssigningBit

means the expression should be evaluated before any assignement

const unsigned int EvalBeforeNestingBit

means the expression should be evaluated by the calling expression

const unsigned int LinearAccessBit

Short version: means the expression can be seen as 1D vector.

Long version: means that one can access the coefficients of this expression by coeff(int), and coeffRef(int) in the case of a lvalue expression. These index-based access methods are guaranteed to not have to do any runtime computation of a (row, col)-pair from the index, so that it is guaranteed that whenever it is available, index-based access is at least as fast as (row,col)-based access. Expressions for which that isn't possible don't have the LinearAccessBit.

If both PacketAccessBit and LinearAccessBit are set, then the packets of this expression can be accessed by packet(int), and writePacket(int) in the case of a lvalue expression.

Typically, all vector expressions have the LinearAccessBit, but there is one exception: Product expressions don't have it, because it would be troublesome for vectorization, even when the Product is a vector expression. Thus, vector Product expressions allow index-based coefficient access but not index-based packet access, so they don't have the LinearAccessBit.

const unsigned int LowerTriangularBit

means the strictly upper triangular part is 0

const unsigned int PacketAccessBit

Short version: means the expression might be vectorized

Long version: means that the coefficients can be handled by packets and start at a memory location whose alignment meets the requirements of the present CPU architecture for optimized packet access. In the fixed-size case, there is the additional condition that the total size of the coefficients array is a multiple of the packet size, so that it is possible to access all the coefficients by packets. In the dynamic-size case, there is no such condition on the total size, so it might not be possible to access the few last coeffs by packets.

Note:
This bit can be set regardless of whether vectorization is actually enabled. To check for actual vectorizability, see ActualPacketAccessBit.
const unsigned int RowMajorBit

for a matrix, this means that the storage order is row-major. If this bit is not set, the storage order is column-major. For an expression, this determines the storage order of the matrix created by evaluation of that expression.

const unsigned int SelfAdjointBit

means the matrix is selfadjoint (M=M*).

const unsigned int SparseBit

means the expression includes sparse matrices and the sparse path has to be taken.

const unsigned int UnitDiagBit

means all diagonal coefficients are equal to 1

const unsigned int UpperTriangularBit

means the strictly lower triangular part is 0

const unsigned int ZeroDiagBit

means all diagonal coefficients are equal to 0

Generated on Sun Aug 1 22:06:51 2010 for Eigen by  doxygen 1.6.3