Re: [eigen] Interesting C++ standard proposal |

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Hi,
(browsing through unanswered mails ...)
On 11.09.2013 09:00, Hauke Heibel wrote:

I just thought some of you might be interested in this proposal:
http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2013/n3748.pdf

`Yes, that looks interesting, but as you said, even if this gets accepted
``it will take a long time until we can profit from it.
``Until then, we must rely on Gael to implement the expression-evaluator
``and educate our users that storing expression trees is often not the
``most efficient solution (but that depends on the expression and how
``often it is used).
`
E.g.
MatrixXd A, B, C, X, Y, Z;
auto A_plus_B = A+B; // usually ok (not always ...)
auto A_times_B= A*B; // in many cases (A*B).eval() is better
X = A_plus_B + C; // more efficient than evaluating A+B.
Y.noAlias() = C + A_times_B; // currently fails, but efficient later.
// fails at the moment and inefficient (product gets evaluated twice):
Z.noAlias() = A_times_B + A_times_B.transpose();
Christoph
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Dipl.-Inf., Dipl.-Math. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
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