diff --git a/Advanced/Linear Maps/main.tex b/Advanced/Linear Maps/main.tex index dc0c404..6dfb23c 100755 --- a/Advanced/Linear Maps/main.tex +++ b/Advanced/Linear Maps/main.tex @@ -44,7 +44,7 @@ \vfill \problem{} - Is the set of all linear maps a vector space? + Show that the set of all linear maps is a vector space. \vfill \end{document} \ No newline at end of file diff --git a/Advanced/Linear Maps/parts/3 matrices.tex b/Advanced/Linear Maps/parts/3 matrices.tex index fe62669..94dac64 100644 --- a/Advanced/Linear Maps/parts/3 matrices.tex +++ b/Advanced/Linear Maps/parts/3 matrices.tex @@ -11,14 +11,8 @@ A = $$ The above matrix has two rows and three columns. It is thus a $2 \times 3$ matrix. -\problem{} -Draw a $3 \times 2$ matrix. +We can define the product of a matrix $A$ and a vector $v$ as follows: -\vfill - -\definition{} -We can define the \say{product\footnotemark{}} of a matrix $A$ and a vector $v$: -\footnotetext{This is an uncommon word to use in this context. You will soon see why.} $$ Av = \begin{bmatrix} @@ -34,7 +28,7 @@ Av = 4a + 5b + 6c \end{bmatrix} $$ -Look closely. Each element of the resulting $2 \times 1$ matrix is the dot product of a row of $A$ with $v$: +Each element of the resulting $2 \times 1$ matrix is the dot product of a row of $A$ with $v$: $$ Av = @@ -56,6 +50,13 @@ $$ Naturally, a vector can only be multiplied by a matrix if the number of rows in the vector equals the number of columns in the matrix. + +\problem{} +Say you multiply a size-$m$ vector by an $m \times n$ matrix. What is the size of your result? + +\vfill + + \problem{} Compute the following: @@ -156,7 +157,7 @@ It is a bit more interesting to think of matrix-vector multiplication in the fol \vspace{2mm} -Be aware that this is only a model for intuition. \\ +This is only a model for intuition, though. \\ Make sure you understand the dot product definition on the previous page. \vspace{5mm} @@ -167,24 +168,15 @@ Conversely, every $n \times m$ matrix represents a liner map $T: \mathbb{R}^n \t \vspace{2mm} -In other words, \textbf{matrices are linear transformations}. \\ -If you only learn only one thing today, this should be it. - -\vfill - +In other words, \textbf{matrices are linear transformations}. \problem{} Show that the transformation $T: \mathbb{R}^n \to \mathbb{R}^m$ defined by $T(v) = Av$ is linear. \\ -Before you start, answer the following questions: -\begin{itemize} - \item What is $A$? - \item What is $v$? - \item What are their sizes? -\end{itemize} +\hint{What is $A$? What is $v$? What are their sizes?} \vfill \problem{} -Show that any linear transformation can be written as a matrix. +Show that any linear transformation $T: \mathbb{R}^n \to \mathbb{R}^m$ can be written as $T(v) = Av$. \vfill \pagebreak @@ -197,7 +189,7 @@ Show that $\mathbb{P}^n$, the set of polynomials of degree $n$, is a vector spac \problem{} Consider the transformation $D: \mathbb{P}^3 \to \mathbb{P}^2$ defined by $D(p) = \frac{d}{dx}p$. \\ Find a matrix that corresponds to $D$. \\ -\hint{$\mathbb{P}^3$ and $\mathbb{R}^4$ are isomorphic. How solutions?} +\hint{$\mathbb{P}^3$ and $\mathbb{R}^4$ are isomorphic. How so?} \vfill