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\newcommand{\hmwkClass}{INF 1004 Mathematics 2}
\newcommand{\hmwkTitle}{Tutorial\ \#7}
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\begin{document}

\maketitle
\pagebreak

\begin{homeworkProblem}
    Compute the euclidean vector norm for vectors
$$
\begin{bmatrix}
    1,0,2
\end{bmatrix}
,
\begin{bmatrix}
    3,4
\end{bmatrix}
,
\begin{bmatrix}
    -7,2,-4, \sqrt{12}
\end{bmatrix}
$$

\solution

\part

$$\lVert [1,0,2] \rVert_2 = \sqrt{1^2 + 0^2 + 2^2} = \boxed{\sqrt{5}}$$

\part

$$\lVert [3,4] \rVert_2 = \sqrt{3^2 + 4^2} = \sqrt{25} = \boxed{5}$$

\part

$$
\begin{align*}
    \lVert [-7,2,-4, \sqrt{12}] \rVert_2 &= \sqrt{(-7)^2 + 2^2 + (-4)^2 + \sqrt{12}^2} \\
                                         &= \sqrt{49 + 4 + 16 + 12} \\
                                         &= \sqrt{81}\\
                                         &= \boxed{9}
\end{align*}
$$
\end{homeworkProblem}

\pagebreak

\begin{homeworkProblem}
Compute the corresponding unit length vector for these:
$$
\begin{bmatrix}
    3,4
\end{bmatrix}
,
\begin{bmatrix}
    -1,-2,3
\end{bmatrix}
,
\begin{bmatrix}
    -7,2,-4, \sqrt{12}
\end{bmatrix}
$$

\solution

$$
\lVert v \rVert_2 = 1
$$
$$
v \neq 0 \implies \frac{v}{\lVert v \rVert_2}
$$

\part

$$
\begin{align*}
    \frac{[3,4]}{\lVert [3,4] \rVert_2} &= \frac{[3,4]}{5} \\
                                        &= \frac{1}{5} \begin{bmatrix} 3,4 \end{bmatrix} \\
                                        &= \boxed{\begin{bmatrix} \frac{3}{5}, \frac{4}{5} \end{bmatrix}}
\end{align*}
$$

\part

$$
\begin{align*}
    \frac{[-1,-2,3]}{\lVert [-1,-2,3] \rVert_2} &= \frac{[-1,-2,3]}{\sqrt{1^2 + 4^2 + 9^2}} \\
                                                &= \frac{1}{\sqrt{14}} \begin{bmatrix} -1,-2,3 \end{bmatrix} \\
                                                &= \boxed{\begin{bmatrix} -\frac{1}{\sqrt{14}}, -\frac{2}{\sqrt{14}}, \frac{3}{\sqrt{14}} \end{bmatrix}}
\end{align*}
$$

\part

$$
\begin{align*}
    \frac{[-7,2,-4, \sqrt{12}]}{\lVert [-7,2,-4, \sqrt{12}] \rVert_2} &= \frac{[-7,2,-4, \sqrt{12}]}{\sqrt{(-7)^2 + 2^2 + (-4)^2 + \sqrt{12}^2}} \\
                                                                    &= \frac{1}{\sqrt{81}} \begin{bmatrix} -7,2,-4, \sqrt{12} \end{bmatrix} \\
                                                                    &= \frac{1}{9} \begin{bmatrix} -7,2,-4,\sqrt{12}\end{bmatrix}\\
                                                                    &= \boxed{\begin{bmatrix} -\frac{7}{9}, \frac{2}{9}, -\frac{4}{9}, \frac{\sqrt{12}}{9} \end{bmatrix}}
\end{align*}
$$
\end{homeworkProblem}

\pagebreak

\begin{homeworkProblem}
    Compute the inner product between these vectors and their angle in degrees:
$$
\begin{bmatrix}
    3,-2,2
\end{bmatrix}
,
\begin{bmatrix}
1,2,2
\end{bmatrix}
$$

Compute the inner product between these vectors and their angle in degrees:
$$
\begin{bmatrix}
1,0,1
\end{bmatrix}
,
\begin{bmatrix}
    2,1,-2
\end{bmatrix}
,
\begin{bmatrix}
    \frac{1}{2\sqrt{2}}
    , -\frac{\sqrt{3}}{2}
    , \frac{1}{2\sqrt{2}}}
\end{bmatrix}
$$

\solution

    $$\frac{u}{\lVert u \rVert_2} \cdot \frac{v}{\lVert v \rVert_2} = \cos(\angle (u,v))$$

\part

$$
\begin{align*}
    \langle [3,-2,2], [1,2,2] \rangle &= 3 \cdot 1 + (-2) \cdot 2 + 2 \cdot 2 \\
                                      &= 3 + (-4) + 4 \\
                                      &= \boxed{3}
\end{align*}
$$

Angle:\\

Let $u$ be $\begin{bmatrix}3,-2,2\end{bmatrix}$ and $v$ be $\begin{bmatrix}1,2,2\end{bmatrix}$\\

$$
\begin{align*}
    \cos(\angle (u,v)) &= \frac{\langle u,v \rangle}{\lVert u \rVert_2 \cdot \lVert v \rVert_2} \\
                       &= \frac{\begin{bmatrix}3,-2,2\end{bmatrix} \cdot \begin{bmatrix}1,2,2\end{bmatrix}}{\lVert \begin{bmatrix}3,-2,2\end{bmatrix} \rVert_2 \cdot \lVert \begin{bmatrix}1,2,2\end{bmatrix} \rVert_2} \\
                       &= \frac{3}{\sqrt{17}\cdot\sqrt{9}} \\
                       &= \frac{3}{\sqrt{153}} \\\\
           \angle (u,v) &= \cos^{-1}(\frac{3}{\sqrt{153}}) \\
                        &= \boxed{75.96^{\circ}}
\end{align*}
$$

\pagebreak

\part

$$
\begin{align*}
    \langle [1,0,1], [2,1,-2] \rangle &= 1 \cdot 2 + 0 \cdot 1 + 1 \cdot (-2) \\
                                      &= 2 + 0 + (-2) \\
                                      &= \boxed{0}
\end{align*}
$$

Angle:\\

Let $u$ be $\begin{bmatrix}1,0,1\end{bmatrix}$ and $v$ be $\begin{bmatrix}2,1,-2\end{bmatrix}$\\

$$
\begin{align*}
    \cos(\angle (u,v)) &= \frac{\langle u,v \rangle}{\lVert u \rVert_2 \cdot \lVert v \rVert_2} \\ &= \frac{\begin{bmatrix}1,0,1\end{bmatrix} \cdot \begin{bmatrix}2,1,-2\end{bmatrix}}{\lVert \begin{bmatrix}1,0,1\end{bmatrix} \rVert_2 \cdot \lVert \begin{bmatrix}2,1,-2\end{bmatrix} \rVert_2} \\
                       &= \frac{0}{\sqrt{2}\cdot\sqrt{6}} \\
                       &= 0 \\\\
           \angle (u,v) &= \cos^{-1}(0) \\
                        &= \boxed{90^{\circ}}
\end{align*}
$$

\part

$$
\begin{align}
    [2,1,2], \left[\frac{1}{2\sqrt{2}}, -\frac{\sqrt{3}}{2}, \frac{1}{2\sqrt{2}}\right] &= \left(2 \cdot \frac{1}{2\sqrt(2)}\right) + \left(1 \cdot -\frac{\sqrt{3}}{2}\right) + \left(2 \cdot \frac{1}{2\sqrt(2)}\right) \\
                                                                                        &= \frac{1}{\sqrt{2}} - \frac{\sqrt{2}}{2} + \frac{1}{\sqrt{2}}\\
                                                                                        &= \frac{\sqrt{2}}{2}
\end{align}
$$

Angle:\\

Let $u$ be $\begin{bmatrix}2,1,2\end{bmatrix}$ and $v$ be $\begin{bmatrix}\frac{1}{2\sqrt{2}}, -\frac{\sqrt{3}}{2}, \frac{1}{2\sqrt{2}}\end{bmatrix}$\\

$$
\begin{align*}
    \cos(\angle (u,v)) &= \frac{\langle u,v \rangle}{\lVert u \rVert_2 \cdot \lVert v \rVert_2} \\
                       &= \frac{\begin{bmatrix}2,1,2\end{bmatrix} \cdot \begin{bmatrix}\frac{1}{2\sqrt{2}}, -\frac{\sqrt{3}}{2}, \frac{1}{2\sqrt{2}}\end{bmatrix}}{\lVert \begin{bmatrix}2,1,2\end{bmatrix} \rVert_2 \cdot \lVert \begin{bmatrix}\frac{1}{2\sqrt{2}}, -\frac{\sqrt{3}}{2}, \frac{1}{2\sqrt{2}}\end{bmatrix} \rVert_2} \\
                       &= \frac{\frac{\sqrt{2}}{2}}{\sqrt{9}\cdot\sqrt{1}}\\
                       &= \frac{\frac{\sqrt{2}}{2}}{\sqrt{9}}\\
                       &= \frac{\sqrt{2}}{2\sqrt{9}}\\
                       &= \cos^{-1}(\frac{\sqrt{2}}{2\sqrt{9}})\\
                       &= \boxed{76.36^{\circ}}
\end{align*}
$$

\end{homeworkProblem}

\pagebreak

\begin{homeworkProblem}
    \begin{itemize}
        \item What is the projection of $\begin{bmatrix}5,2 \end{bmatrix}$ onto the subspace spanned by vector $\begin{bmatrix} 1,1 \end{bmatrix}$?
        \item What is the projection of $\begin{bmatrix}0,2,1 \end{bmatrix}$ onto the subspace spanned by vector $\begin{bmatrix} 1,-1,-1 \end{bmatrix}$?
        \item Project $\begin{bmatrix} 5,2 \end{bmatrix}$ onto the subspace spanned by vectors $\begin{bmatrix} 2,3 \end{bmatrix}$, $\begin{bmatrix}1,1 \end{bmatrix}$
        \item What is the projection of $\begin{bmatrix} 1,-1,1 \end{bmatrix}$ onto the subspace spanned by vector $\begin{bmatrix} 1,1,1 \end{bmatrix}$ onto the subspace spanned by vectors  $\begin{bmatrix} 0,0,-1 \end{bmatrix}, \begin{bmatrix} 2,0,1 \end{bmatrix}$? Hint: this one is more tricky. Reason: $\begin{bmatrix} 0,-1,-1 \end{bmatrix} \cdot \begin{bmatrix}2,0,1\end{bmatrix} \neq 0$
    \end{itemize}

    \solution

    $$ x_{\parallel} v = \frac{x\cdot v}{v\cdot v}v =\left(x\cdot \frac{v}{\lVert v \rVert_2}\right) \frac{v}{\lVert v \rVert_2} $$

    \part

    $$
    \begin{align*}
        \frac{\begin{bmatrix} 5,2 \end{bmatrix} \cdot \begin{bmatrix} 1,1 \end{bmatrix}}{2} \begin{bmatrix} 1,1 \end{bmatrix} &= \frac{7}{2} \begin{bmatrix}1,1\end{bmatrix}\\
    \end{align*}
    $$

    \part

    $$
    \begin{align*}
        \frac{\begin{bmatrix} 0,2,1 \end{bmatrix} \cdot \begin{bmatrix} 1,-1,-1 \end{bmatrix}}{3} \begin{bmatrix} 1,-1,-1 \end{bmatrix} &= \frac{-3}{3} \begin{bmatrix}1,-1,-1\end{bmatrix}\\
                                                                                                                                        &= \begin{bmatrix}-1,1,1\end{bmatrix}
    \end{align*}
    $$

    \part

    $$
    \begin{align*}
        \frac{\begin{bmatrix} 5,2 \end{bmatrix} \cdot \begin{bmatrix} 2,3 \end{bmatrix}}{13} \begin{bmatrix} 2,3 \end{bmatrix} + \frac{\begin{bmatrix} 5,2 \end{bmatrix} \cdot \begin{bmatrix} 1,1 \end{bmatrix}}{2} \begin{bmatrix} 1,1 \end{bmatrix} &= \frac{16}{13} \begin{bmatrix}2,3\end{bmatrix} + \frac{7}{2} \begin{bmatrix}1,1\end{bmatrix}\\
    &= \begin{bmatrix} \frac{32}{13}, \frac{48}{13} \end{bmatrix} + \begin{bmatrix} \frac{7}{2}, \frac{7}{2} \end{bmatrix}\\
    &= \begin{bmatrix} \frac{32+7}{13}, \frac{48+7}{13} \end{bmatrix}\\
    &= \begin{bmatrix} \frac{39}{13}, \frac{55}{13} \end{bmatrix}
    \end{align*}
    $$
\end{homeworkProblem}

\pagebreak

\begin{homeworkProblem}
    Compute these matrix multiplications:
    $$
    \begin{bmatrix}
        2 & 1\\3&-2
    \end{bmatrix}
    \begin{bmatrix}
        -1 &0\\-4&-2
    \end{bmatrix}
    $$
    \\
    $$
    \begin{bmatrix}
        -3\\2\\1
    \end{bmatrix}
    \begin{bmatrix}
        2&4&-2
    \end{bmatrix}
    $$
    \\
    Question: Do you need more of them to practice? If so, you can do at home:\\
    $$
    \begin{bmatrix}
        1&2\\2&4
    \end{bmatrix}
    \begin{bmatrix}
        3&0&1\\0&1&2
    \end{bmatrix}
    $$
    \\
    $$
    \begin{bmatrix}
        0.5&2.5\\-3.5&1.5
    \end{bmatrix}
    \begin{bmatrix}
        6\\4
    \end{bmatrix}
    $$

    \solution

    \part

    $$
    \begin{bmatrix}
        2 & 1\\3&-2
    \end{bmatrix}
    \begin{bmatrix}
        -1 &0\\-4&-2
    \end{bmatrix}
    =
    \begin{bmatrix}
        2\cdot(-1)+1\cdot(-4) & 2\cdot0+1\cdot(-2)\\3\cdot(-1)+(-2)\cdot(-4) & 3\cdot0+(-2)\cdot(-2)
    \end{bmatrix}
    =
    \begin{bmatrix}
        -6 & -2\\5 & 4
    \end{bmatrix}
    $$
    \\
    $$
    \begin{bmatrix}
        -3\\2\\1
    \end{bmatrix}
    \begin{bmatrix}
        2&4&-2
    \end{bmatrix}
    =
    \begin{bmatrix}
        -3\cdot2 & -3\cdot4 & -3\cdot(-2)\\2\cdot2 & 2\cdot4 & 2\cdot(-2)\\1\cdot2 & 1\cdot4 & 1\cdot(-2)
    \end{bmatrix}
    =
    \begin{bmatrix}
        -6 & -12 & 6\\4 & 8 & -4\\2 & 4 & -2
    \end{bmatrix}
    $$

    \part

    $$
    \begin{bmatrix}
        1&2\\2&4
    \end{bmatrix}
    \begin{bmatrix}
        3&0&1\\0&1&2
    \end{bmatrix}
    =
    \begin{bmatrix}
        1\cdot3+2\cdot0 & 1\cdot0+2\cdot1 & 1\cdot1+2\cdot2\\2\cdot3+4\cdot0 & 2\cdot0+4\cdot1 & 2\cdot1+4\cdot2
    \end{bmatrix}
    =
    \begin{bmatrix}
        3 & 2 & 4\\6 & 4 & 10
    \end{bmatrix}
    $$
    \\
    $$
    \begin{bmatrix}
        0.5&2.5\\-3.5&1.5
    \end{bmatrix}
    \begin{bmatrix}
        6\\4
    \end{bmatrix}
    =
    \begin{bmatrix}
        0.5\cdot6+2.5\cdot4 \\ 0.5\cdot4+2.5\cdot6
    \end{bmatrix}
    =
    \begin{bmatrix}
        13 \\ -15
    \end{bmatrix}
    $$


\end{homeworkProblem}

\pagebreak

\begin{homeworkProblem}

    \begin{itemize}
        \item Project $\begin{bmatrix} 5,2 \end{bmatrix}$ onto the orthogonal space of vector $\begin{bmatrix} 2,-3 \end{bmatrix}$
        \item Project $\begin{bmatrix} 1,-1,3 \end{bmatrix}$ onto the orthogonal space of vector $\begin{bmatrix} -3,1,1\end{bmatrix}$
        \item Project $\begin{bmatrix} 1,-1,3,1 \end{bmatrix}$ onto the orthogonal space of vector $\begin{bmatrix} -2,2,0,0\end{bmatrix}$, $\begin{bmatrix} 0,0,\sqrt{2}, \sqrt{2}\end{bmatrix}$
    \end{itemize}

    \solution

    \part

    $$
    \begin{align*}
        \begin{bmatrix} 5,2 \end{bmatrix} \cdot \begin{bmatrix} 2,-3 \end{bmatrix} \cdot \frac{\begin{bmatrix} 2,-3 \end{bmatrix}}{\lVert \begin{bmatrix} 2,-3 \end{bmatrix} \rVert^2} &= \frac{2\cdot5+(-3)\cdot2}{\lVert \begin{bmatrix} 2,-3 \end{bmatrix} \rVert^2} \\
        &= \frac{13}{13} \\
        &= 1
    \end{align*}
    $$

    \part

    $$
    \begin{align*}
        \begin{bmatrix} 1,-1,3 \end{bmatrix} \cdot \begin{bmatrix} -3,1,1\end{bmatrix} \cdot \frac{\begin{bmatrix} -3,1,1\end{bmatrix}}{\lVert \begin{bmatrix} -3,1,1\end{bmatrix} \rVert^2} &= \frac{(-3)\cdot1+1\cdot(-1)+1\cdot3}{\lVert \begin{bmatrix} -3,1,1\end{bmatrix} \rVert^2} \\
        &= \frac{1}{\sqrt{13}} \\
        &= \frac{1}{\sqrt{13}}
    \end{align*}
    $$

    \part

    $$
    \begin{align*}
        \begin{bmatrix} 1,-1,3,1 \end{bmatrix} \cdot \begin{bmatrix} -2,2,0,0\end{bmatrix} \cdot \frac{\begin{bmatrix} -2,2,0,0\end{bmatrix}}{\lVert \begin{bmatrix} -2,2,0,0\end{bmatrix} \rVert^2} &= \frac{(-2)\cdot1+2\cdot(-1)+0\cdot3+0\cdot1}{\lVert \begin{bmatrix} -2,2,0,0\end{bmatrix} \rVert^2} \\
        &= \frac{1}{\sqrt{8}} \\
        &= \frac{1}{\sqrt{8}}
    \end{align*}
    $$

    $$
    \begin{align*}
        \begin{bmatrix} 1,-1,3,1 \end{bmatrix} \cdot \begin{bmatrix} 0,0,\sqrt{2}, \sqrt{2}\end{bmatrix} \cdot \frac{\begin{bmatrix} 0,0,\sqrt{2}, \sqrt{2}\end{bmatrix}}{\lVert \begin{bmatrix} 0,0,\sqrt{2}, \sqrt{2}\end{bmatrix} \rVert^2} &= \frac{0\cdot1+0\cdot(-1)+\sqrt{2}\cdot3+\sqrt{2}\cdot1}{\lVert \begin{bmatrix} 0,0,\sqrt{2}, \sqrt{2}\end{bmatrix} \rVert^2} \\
        &= \frac{3+\sqrt{2}}{\sqrt{2}} \\
        &= \frac{3+\sqrt{2}}{\sqrt{2}}
    \end{align*}
    $$

\end{homeworkProblem}

\pagebreak

\begin{homeworkProblem}
    Run Gram-Schmid-orthogonalization on the vectors
    $$\begin{bmatrix} 12,12,6 \end{bmatrix}, \begin{bmatrix} 2,-2,4 \end{bmatrix}, \begin{bmatrix} -2,-2,1 \end{bmatrix}$$

    \solution

    \part

    $$

    \begin{align*}
        \begin{bmatrix} 12,12,6 \end{bmatrix} &= \begin{bmatrix} 12,12,6 \end{bmatrix} \\
        \begin{bmatrix} 2,-2,4 \end{bmatrix} &= \begin{bmatrix} 2,-2,4 \end{bmatrix} - \frac{2\cdot12+(-2)\cdot12+4\cdot6}{\lVert \begin{bmatrix} 12,12,6 \end{bmatrix} \rVert^2} \cdot \begin{bmatrix} 12,12,6 \end{bmatrix} \\
        &= \begin{bmatrix} 2,-2,4 \end{bmatrix} - \frac{144}{144} \cdot \begin{bmatrix} 12,12,6 \end{bmatrix} \\
        &= \begin{bmatrix} 2,-2,4 \end{bmatrix} - \begin{bmatrix} 12,12,6 \end{bmatrix} \\
        &= \begin{bmatrix} -10,-14,-2 \end{bmatrix} \\
        \begin{bmatrix} -2,-2,1 \end{bmatrix} &= \begin{bmatrix} -2,-2,1 \end{bmatrix} - \frac{(-2)\cdot12+(-2)\cdot12+1\cdot6}{\lVert \begin{bmatrix} 12,12,6 \end{bmatrix} \rVert^2} \cdot \begin{bmatrix} 12,12,6 \end{bmatrix} \\
        &= \begin{bmatrix} -2,-2,1 \end{bmatrix} - \frac{0}{144} \cdot \begin{bmatrix} 12,12,6 \end{bmatrix} \\
        &= \begin{bmatrix} -2,-2,1 \end{bmatrix} - \begin{bmatrix} 0,0,0 \end{bmatrix} \\
        &= \begin{bmatrix} -2,-2,1 \end{bmatrix}
    \end{align*}

    $$

\end{homeworkProblem}

\pagebreak

\begin{homeworkProblem}
{\large \textbf{Understanding Distances coming from $\ell_p$-norms}}\\

    Coding: plot in python or similar the set of points $x \in \mathbb{R}^2$ usuch that $\lVert x \rVert_p = 1$ for
    \begin{itemize}
        \item $p = 0.2$
        \item $p = 0.5$
        \item $p = 1$
        \item $p = 1.5$
        \item $p = 2$
        \item $p = 4$
        \item $p = 8$
        \item $p = 16$
    \end{itemize}
    Hint: in 2 dimensions for $p=2$ the solution is given by
    $$x(t) = \left(\cos(t), \sin(t)\right)$$
    due to $\cos^2(t) + \sin^2(t) = 1$.

you can use the same idea with different powers. You can start by considering $(\cos^r(t), \sin^r(t))$. One thing to node: $\cos(t)^r + \sin(t)^r$ is not always defined for negative values and certain $r$.\\

For $p \neq 2$, you can consider this, thich deals with the signs:
$$x(t) = (sign(\cos(t))|\cos(t)|^r, sign(\sin(t))|\sin(t)|^r)$$
for the right choice of r. Find out which $r$ is suitable for a general $p > 0$ such that $\lVert x \rVert_p = 1$. Then plot it in python.\\

    \solution

    \part

    $$
    \begin{align*}
        \begin{bmatrix} 1,-1,3,1 \end{bmatrix} \cdot \begin{bmatrix} 1,1,1,1\end{bmatrix} \cdot \frac{\begin{bmatrix} 1,1,1,1\end{bmatrix}}{\lVert \begin{bmatrix} 1,1,1,1\end{bmatrix} \rVert^2} &= \frac{1\cdot1+(-1)\cdot1+3\cdot1+1\cdot1}{\lVert \begin{bmatrix} 1,1,1,1\end{bmatrix} \rVert^2} \\
        &= \frac{4}{2} \\
        &= 2
    \end{align*}
    $$


\end{homeworkProblem}
\end{document}
