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The the product of two matrices AB is defined if and only if the number of columns n in A equals the number of rows m in B. But what if A is a 1x1 matrix (i.e. a scalar) and B is some m x n matrix where m > 1?

Armadillo
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    A $1 \times 1$ matrix is not a scalar. – Clement Yung Jun 24 '20 at 16:48
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    You'll tire yourself out with questions like that. The easy answer is "don't sweat the small details." Imagine scalars as not being matrices at all (even if they could be interpreted as matrices) and make a distinction in your mind between $1\times 1$ matrices and scalars. Be aware that you can freely swap between interpretations as is convenient to you for ease of writing. This is like how we might think of the number $1$ as the natural number, as the integer, as the rational number, as the real number, etc... depending on context, and freely switch between which we are referring to – JMoravitz Jun 24 '20 at 16:50
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    Matrix multiplication and scalar multiplication are not the same operations. – B. Goddard Jun 24 '20 at 16:50
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    See also this post – Ben Grossmann Jun 24 '20 at 17:11
  • Thank you all for your comments (+1), these all help to answer my question. – Armadillo Jun 24 '20 at 19:01

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