make pdf file generation work
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@@ -98,13 +98,13 @@ In dimension $m=3$, the **binormal** vector, $\hat{B}$, is the unit vector $\hat
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The [Frenet-Serret]() formulas define the **curvature**, $\kappa$, and the **torsion**, $\tau$, by
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$$
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\begin{align}
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\begin{align*}
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\frac{d\hat{T}}{ds} &= & \kappa \hat{N} &\\
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\frac{d\hat{N}}{ds} &= -\kappa\hat{T} & & + \tau\hat{B}\\
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\frac{d\hat{B}}{ds} &= & -\tau\hat{N}&
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\end{align}
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$$
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\end{align*}
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These formulas apply in dimension $m=2$ with $\hat{B}=\vec{0}$.
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@@ -121,14 +121,14 @@ The chain rule says $(\vec{r}(g(t))' = \vec{r}'(g(t)) g'(t)$.
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A scalar function, $f:R^n\rightarrow R$, $n > 1$ has a **partial derivative** defined. For $n=2$, these are:
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$$
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\begin{align}
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\begin{align*}
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\frac{\partial{f}}{\partial{x}}(x,y) &=
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\lim_{h\rightarrow 0} \frac{f(x+h,y)-f(x,y)}{h}\\
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\frac{\partial{f}}{\partial{y}}(x,y) &=
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\lim_{h\rightarrow 0} \frac{f(x,y+h)-f(x,y)}{h}.
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\end{align}
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$$
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\end{align*}
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The generalization to $n>2$ is clear - the partial derivative in $x_i$ is the derivative of $f$ when the *other* $x_j$ are held constant.
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@@ -198,14 +198,13 @@ For $F=\langle f_1, f_2, \dots, f_m\rangle$ the total derivative is the **Jacob
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$$
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J_f = \left[
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\begin{align}{}
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J_f =
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\begin{bmatrix}
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\frac{\partial f_1}{\partial x_1} &\quad \frac{\partial f_1}{\partial x_2} &\dots&\quad\frac{\partial f_1}{\partial x_n}\\
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\frac{\partial f_2}{\partial x_1} &\quad \frac{\partial f_2}{\partial x_2} &\dots&\quad\frac{\partial f_2}{\partial x_n}\\
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&&\vdots&\\
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\frac{\partial f_m}{\partial x_1} &\quad \frac{\partial f_m}{\partial x_2} &\dots&\quad\frac{\partial f_m}{\partial x_n}
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\end{align}
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\right].
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\end{bmatrix}.
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$$
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This can be viewed as being comprised of row vectors, each being the individual gradients; or as column vectors each being the vector of partial derivatives for a given variable.
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@@ -225,7 +224,7 @@ A scalar function $f:R^n \rightarrow R$ and a parameterized curve $\vec{r}:R\rig
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$$
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d_f(\vec{r}) d_\vec{r} = \nabla{f}(\vec{r}(t))' \vec{r}'(t) =
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d_f(\vec{r}) d\vec{r} = \nabla{f}(\vec{r}(t))' \vec{r}'(t) =
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\nabla{f}(\vec{r}(t)) \cdot \vec{r}'(t),
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$$
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@@ -356,29 +355,29 @@ $$
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In two dimensions, we have the following interpretations:
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$$
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\begin{align}
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\begin{align*}
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\iint_R dA &= \text{area of } R\\
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\iint_R \rho dA &= \text{mass with constant density }\rho\\
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\iint_R \rho(x,y) dA &= \text{mass of region with density }\rho\\
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\frac{1}{\text{area}}\iint_R x \rho(x,y)dA &= \text{centroid of region in } x \text{ direction}\\
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\frac{1}{\text{area}}\iint_R y \rho(x,y)dA &= \text{centroid of region in } y \text{ direction}
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\end{align}
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$$
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\end{align*}
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In three dimensions, we have the following interpretations:
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$$
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\begin{align}
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\begin{align*}
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\iint_VdV &= \text{volume of } V\\
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\iint_V \rho dV &= \text{mass with constant density }\rho\\
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\iint_V \rho(x,y) dV &= \text{mass of volume with density }\rho\\
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\frac{1}{\text{volume}}\iint_V x \rho(x,y)dV &= \text{centroid of volume in } x \text{ direction}\\
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\frac{1}{\text{volume}}\iint_V y \rho(x,y)dV &= \text{centroid of volume in } y \text{ direction}\\
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\frac{1}{\text{volume}}\iint_V z \rho(x,y)dV &= \text{centroid of volume in } z \text{ direction}
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\end{align}
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$$
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\end{align*}
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To compute integrals over non-box-like regions, Fubini's theorem may be utilized. Alternatively, a **transformation** of variables
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