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Set cost of conjugate to 0 (in practice it boils down to a no-op).

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This is also important to make sure that A.conjugate() * B.conjugate() does not evaluate
its arguments into temporaries (e.g., if A and B are fixed and small, or * fall back to lazyProduct)
This commit is contained in:
Gael Guennebaud 2019-02-18 14:43:07 +01:00
parent 512b74aaa1
commit c69d0d08d0
2 changed files with 11 additions and 1 deletions
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10
Eigen/src/Core/functors/UnaryFunctors.h
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@ -117,7 +117,15 @@ template<typename Scalar>
struct functor_traits<scalar_conjugate_op<Scalar> >
{
enum {
Cost = NumTraits<Scalar>::IsComplex ? NumTraits<Scalar>::AddCost : 0,
Cost = 0,
// Yes the cost is zero even for complexes because in most cases for which
// the cost is used, conjugation turns to be a no-op. Some examples:
// cost(a*conj(b)) == cost(a*b)
// cost(a+conj(b)) == cost(a+b)
// <etc.
// If we don't set it to zero, then:
// A.conjugate().lazyProduct(B.conjugate())
// will bake its operands. We definitely don't want that!
PacketAccess = packet_traits<Scalar>::HasConj
};
};

2
test/product_notemporary.cpp
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@ -134,7 +134,9 @@ template<typename MatrixType> void product_notemporary(const MatrixType& m)
VERIFY_EVALUATION_COUNT( m3.noalias() = m1.block(r0,r0,r1,r1).template triangularView<UnitUpper>() * m2.block(r0,c0,r1,c1), 1);
// Zero temporaries for lazy products ...
m3.setRandom(rows,cols);
VERIFY_EVALUATION_COUNT( Scalar tmp = 0; tmp += Scalar(RealScalar(1)) / (m3.transpose().lazyProduct(m3)).diagonal().sum(), 0 );
VERIFY_EVALUATION_COUNT( m3.noalias() = m1.conjugate().lazyProduct(m2.conjugate()), 0);
// ... and even no temporary for even deeply (>=2) nested products
VERIFY_EVALUATION_COUNT( Scalar tmp = 0; tmp += Scalar(RealScalar(1)) / (m3.transpose() * m3).diagonal().sum(), 0 );