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Diffstat (limited to 'source/know/concept/laplace-transform')
-rw-r--r-- | source/know/concept/laplace-transform/index.md | 37 |
1 files changed, 19 insertions, 18 deletions
diff --git a/source/know/concept/laplace-transform/index.md b/source/know/concept/laplace-transform/index.md index 5b834c3..c7f352a 100644 --- a/source/know/concept/laplace-transform/index.md +++ b/source/know/concept/laplace-transform/index.md @@ -9,9 +9,9 @@ layout: "concept" --- The **Laplace transform** is an integral transform -that losslessly converts a function $f(t)$ of a real variable $t$, -into a function $\tilde{f}(s)$ of a complex variable $s$, -where $s$ is sometimes called the **complex frequency**, +that losslessly converts a function $$f(t)$$ of a real variable $$t$$, +into a function $$\tilde{f}(s)$$ of a complex variable $$s$$, +where $$s$$ is sometimes called the **complex frequency**, analogously to the [Fourier transform](/know/concept/fourier-transform/). The transform is defined as follows: @@ -23,14 +23,14 @@ $$\begin{aligned} } \end{aligned}$$ -Depending on $f(t)$, this integral may diverge. -This is solved by restricting the domain of $\tilde{f}(s)$ -to $s$ where $\mathrm{Re}\{s\} > s_0$, -for an $s_0$ large enough to compensate for the growth of $f(t)$. +Depending on $$f(t)$$, this integral may diverge. +This is solved by restricting the domain of $$\tilde{f}(s)$$ +to $$s$$ where $$\mathrm{Re}\{s\} > s_0$$, +for an $$s_0$$ large enough to compensate for the growth of $$f(t)$$. -The **inverse Laplace transform** $\hat{\mathcal{L}}{}^{-1}$ involves complex integration, +The **inverse Laplace transform** $$\hat{\mathcal{L}}{}^{-1}$$ involves complex integration, and is therefore a lot more difficult to calculate. -Fortunately, it is usually avoidable by rewriting a given $s$-space expression +Fortunately, it is usually avoidable by rewriting a given $$s$$-space expression using [partial fraction decomposition](/know/concept/partial-fraction-decomposition/), and then looking up the individual terms. @@ -47,7 +47,7 @@ $$\begin{aligned} } \end{aligned}$$ -This property generalizes nicely to higher-order derivatives of $s$, so: +This property generalizes nicely to higher-order derivatives of $$s$$, so: $$\begin{aligned} \boxed{ @@ -60,7 +60,7 @@ $$\begin{aligned} <label for="proof-dv-s">Proof</label> <div class="hidden" markdown="1"> <label for="proof-dv-s">Proof.</label> -The exponential $\exp(- s t)$ is the only thing that depends on $s$ here: +The exponential $$\exp(- s t)$$ is the only thing that depends on $$s$$ here: $$\begin{aligned} \dvn{n}{\tilde{f}}{s} @@ -69,11 +69,12 @@ $$\begin{aligned} &= \int_0^\infty (-t)^n f(t) \exp(- s t) \dd{t} = (-1)^n \hat{\mathcal{L}}\{t^n f(t)\} \end{aligned}$$ + </div> </div> The Laplace transform of a derivative introduces the initial conditions into the result. -Notice that $f(0)$ is the initial value in the original $t$-domain: +Notice that $$f(0)$$ is the initial value in the original $$t$$-domain: $$\begin{aligned} \boxed{ @@ -92,17 +93,17 @@ $$\begin{aligned} } \end{aligned}$$ -Where $f^{(n)}(t)$ is shorthand for the $n$th derivative of $f(t)$, -and $f^{(0)}(t) = f(t)$. -As an example, $\hat{\mathcal{L}}\{f'''(t)\}$ becomes -$- f''(0) - s f'(0) - s^2 f(0) + s^3 \tilde{f}(s)$. +Where $$f^{(n)}(t)$$ is shorthand for the $$n$$th derivative of $$f(t)$$, +and $$f^{(0)}(t) = f(t)$$. +As an example, $$\hat{\mathcal{L}}\{f'''(t)\}$$ becomes +$$- f''(0) - s f'(0) - s^2 f(0) + s^3 \tilde{f}(s)$$. <div class="accordion"> <input type="checkbox" id="proof-dv-t"/> <label for="proof-dv-t">Proof</label> <div class="hidden" markdown="1"> <label for="proof-dv-t">Proof.</label> -We integrate by parts and use the fact that $\lim_{x \to \infty} \exp(-x) = 0$: +We integrate by parts and use the fact that $$\lim_{x \to \infty} \exp(-x) = 0$$: $$\begin{aligned} \hat{\mathcal{L}} \big\{ f^{(n)}(t) \big\} @@ -114,7 +115,7 @@ $$\begin{aligned} \end{aligned}$$ And so on. -By partially integrating $n$ times in total we arrive at the conclusion. +By partially integrating $$n$$ times in total we arrive at the conclusion. </div> </div> |