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Either I'm missing something here or the article is correct. Generally, the first dimension of a matrix corresponds to the rows and the second dimension to the columns. So in the original figure, A is m x k, B is k x n, and C is m x n, and this seems right. See http://en.wikipedia.org/wiki/Matrix_%28mathematics%29#Size

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I think the author revised the figure(s) between the time of the parent comment (by gcr) and your comment. At least, the A * B = C figure's filename seems to imply a revision [1].

EDIT: yep, the figures were revised. Compare the corrected version [1] vs the original [2].

[1] https://petewarden.files.wordpress.com/2015/04/gemm_correcte...

[2] https://petewarden.files.wordpress.com/2015/04/gemm.png

EDIT 2: I completely missed that the author put a notice (about having revised the figures) at the bottom of the post.

Yes, that was my screwup, sorry for any confusion! Despite multiple linear algebra courses, working in 3D graphics for a decade, I haven't internalized the basics of matrix notation. It doesn't help that my usual sandbox (Eigen) is column major by default, which is the wrong in-memory order for my raster-image trained brain to visualize. Funnily enough, I find tensor notation a bit easier, despite being less familiar.

No worries. Also, I found the article very interesting and informative. Thanks!

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