bigMat.block(...).array()mat.array() is slower than mat.array()mat.array()

Submitted by Philippe Marti

Assigned to Nobody

Link to original bugzilla bug (#303)
Version: 3.0
Operating system: Linux

I was doing some simple timings and got suprising timings (at least to me).

with matrices bigMat 500x20, mat1 100x20, mat2 100x20, I compute:

sol = bigMat.block(0,0,100,20).array() * mat2.array();

But compared to:

sol = mat1.array() * mat2.array();

The first computation is ~30% slower on my machine. But:

sol = bigMat.block(0,0,100,20).transpose().array() * mat2.transpose().array()

Is about the same time. Is that really what should be expected ?

Thanks!

Edited Dec 05, 2019 by Eigen Bugzilla