diff --git a/semester3/analysis-ii/cheat-sheet-jh/analysis-ii-cheat-sheet.pdf b/semester3/analysis-ii/cheat-sheet-jh/analysis-ii-cheat-sheet.pdf index 2a4034d..0733df9 100644 Binary files a/semester3/analysis-ii/cheat-sheet-jh/analysis-ii-cheat-sheet.pdf and b/semester3/analysis-ii/cheat-sheet-jh/analysis-ii-cheat-sheet.pdf differ diff --git a/semester3/analysis-ii/cheat-sheet-jh/parts/vectors/differentiation/05_taylor_polynomials.tex b/semester3/analysis-ii/cheat-sheet-jh/parts/vectors/differentiation/05_taylor_polynomials.tex index cda8953..723ea83 100644 --- a/semester3/analysis-ii/cheat-sheet-jh/parts/vectors/differentiation/05_taylor_polynomials.tex +++ b/semester3/analysis-ii/cheat-sheet-jh/parts/vectors/differentiation/05_taylor_polynomials.tex @@ -8,7 +8,6 @@ Let $f : X \rightarrow \R$ with $f \in C^k(X, \R)$ and $y \in X$. The Taylor-Pol \end{align*} \drmvspace\rmvspace -% TODO: Find out what the \partial_1 notation means (likely TA notes 09) where $i$ is a \textit{multi-index}, so: \drmvspace \begin{multicols}{3} @@ -22,14 +21,19 @@ where $i$ is a \textit{multi-index}, so: \end{multicols} \drmvspace\rmvspace +In the input, we have the vector $y$, which is the evaluation point, as well as the vector $x - y$ (where $y$ is the evaluation point again and $x = (x_1, \ldots, x_n)$) + The concept this formula uses is that we iterate through all possible partial derivatives of $f$ and assigns each a multi-index $i$. +Do note that the formula expands to $f(y) + \ldots$, so also include the original function in the sum! + To denote that we want to take the partial derivative $\partial_{112}$, we use $i = (2, 1, 0)$, since we take the derivative of the first variable twice, of the second variable once and never of the third variable. -So the expression is thus now: +This is also the explanation for what the $\partial_1^{i_1}$ means (we take the derivative regarding the first variable $i_1$ times, etc). + +One of the elements of the sum (element with $i = (2, 1, 0)$) is for example: \mrmvspace \begin{align*} - \frac{\partial_{112} f(y) (x_1 - y_1)^2 (x_2 - y_2)^1 (x_3 y_3)^0}{2!1!0!} = \frac{\partial_{112} f(y) (x_1 - y_1)^2 (x_2 - y_2)}{2} + \frac{\partial_{112} f(y) (x_1 - y_1)^2 (x_2 - y_2)^1 (x_3 - y_3)^0}{2!1!0!} = \frac{\partial_{112} f(y) (x_1 - y_1)^2 (x_2 - y_2)}{2} \end{align*} \drmvspace -% TODO: Add example diff --git a/semester3/analysis-ii/cheat-sheet-jh/parts/vectors/differentiation/06_critical_points.tex b/semester3/analysis-ii/cheat-sheet-jh/parts/vectors/differentiation/06_critical_points.tex index 52734bc..ca6c209 100644 --- a/semester3/analysis-ii/cheat-sheet-jh/parts/vectors/differentiation/06_critical_points.tex +++ b/semester3/analysis-ii/cheat-sheet-jh/parts/vectors/differentiation/06_critical_points.tex @@ -20,9 +20,10 @@ To determine the kind of critical point, we need to determine if $H_f(x_0)$ is d To figure out if a matrix is definite, we can compute the eigenvalues. $A$ is positive (negative) definite, if and only if all eigenvalues are greater (lower) than $0$. $A$ is indefinite if and only if it has both positive and negative eigenvalues. $A$ is positive (negative) semi-definite if and only if all eigenvalues are greater (lower) or equal to $0$. +It is positive (negative) definite if and only if all eigenvalues are greater (lower) than $0$ (Compute Eigenvalues using $\det(A - \lambda I) = 0$) -For $2 \times 2$ matrices, we can use the following scheme: +For $2 \times 2$ matrices (i.e. 2D functions), we can use the following scheme (remember that the trace is the sum of the diagonal entries): \begin{center} \begin{tikzpicture}[node distance = 0.3cm and 2cm, >={Stealth[round]}] \node (det) {$\det(A)$};