4 ms·
Totally yes. The mechanistic illustrations of matrix multiplication, including the OP, are easy enough but don't help me with motivation or intuition. I always
by nockupe_2 5y ago
Totally yes. The mechanistic illustrations of matrix multiplication, including the OP, are easy enough but don't help me with motivation or intuition.
I always start with Ax, which is just a linear combination of the columns, like the first figure here https://eli.thegreenplace.net/2015/visualizing-matrix-multiplication-as-a-linear-combination/ https://eli.thegreenplace.net/2015/visualizing-matrix-multip...
For those who want to make their own cheat sheet:
Matrix $\times$ vector is linear combination of the columns:
\begin{align}
Ax &= \begin{pmatrix}
a_{1,1} & a_{1,2}\\
a_{2,1} & a_{2,2}\\
a_{3,1} & a_{3,2}
\end{pmatrix}
\begin{pmatrix}
x_1\\x_2
\end{pmatrix}\\
&= x_1\begin{pmatrix}
a_{1,1}\\
a_{2,1}\\
a_{3,1}\\
\end{pmatrix}
+
x_2\begin{pmatrix}
a_{1,2}\\
a_{2,2}\\
a_{3,2}\\
\end{pmatrix}
\end{align}
Intuitively, this example maps a point in $\mathbb{R}^2$ to $\mathbb{R}^3$
Another way to see $Ax$: Columns of $A$ form a basis, and $x$ is a coordinate vector in that basis.
- vecter 5y agoThe link you posted perfectly depicts what I was saying. It's good to see a clear example of that online, when almost every other resource is showing the dot-product interpretation.