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The $11$th letter of the Greek alphabet.

Minuscule: $\lambda$
Majuscule: $\Lambda$

The $\LaTeX$ code for \(\lambda\) is \lambda .

The $\LaTeX$ code for \(\Lambda\) is \Lambda .

Von Mangoldt Function

$\map \Lambda n$

The von Mangoldt function $\Lambda: \N \to \R$ is defined as:

$\map \Lambda n = \begin{cases} \map \ln p & : \exists m \in \N, p \in \mathbb P: n = p^m \\ 0 & : \text{otherwise} \end{cases}$

where $\mathbb P$ is the set of all prime numbers.

The $\LaTeX$ code for \(\map \Lambda n\) is \map \Lambda n .

Triangle Function

$\map \Lambda x$

The triangle function is the real function $\Lambda: \R \to \R$ defined as:

$\forall x \in \R: \map \Lambda x := \begin {cases} 1 - \size x : & \size x \le 1 \\ 0 : & \size x > 1 \end {cases}$

where $\size x$ denotes the absolute value function.

The $\LaTeX$ code for \(\map \Lambda x\) is \map \Lambda x .

Linear Density


Used to denote the linear density of a given one-dimensional body:

$\lambda = \dfrac m l$


$m$ is the body's mass
$l$ is the body's length.

Poisson Distribution


Used to denote the parameter of a given Poisson distribution:

Let $X$ be a discrete random variable on a probability space $\struct {\Omega, \Sigma, \Pr}$.

Then $X$ has the Poisson distribution with parameter $\lambda$ (where $\lambda > 0$) if and only if:

$\Img X = \set {0, 1, 2, \ldots} = \N$
$\map \Pr {X = k} = \dfrac 1 {k!} \lambda^k e^{-\lambda}$

It is written:

$X \sim \Poisson \lambda$

Order Type of Real Numbers


The order type of $\struct {\R, \le}$ is denoted $\lambda$ (lambda).

Left Regular Representation


Let $\struct {S, \circ}$ be an algebraic structure.

The mapping $\lambda_a: S \to S$ is defined as:

$\forall x \in S: \map {\lambda_a} x = a \circ x$

This is known as the left regular representation of $\struct {S, \circ}$ with respect to $a$.

The $\LaTeX$ code for \(\map {\lambda_a} x\) is \map {\lambda_a} x .

Celestial Longitude


Let $P$ be a point on the celestial sphere.

Let $J$ be a great circle on the celestial sphere passing through $P$ and both of the north ecliptic pole and south ecliptic pole.

The celestial longitude $\lambda$ of $P$ is the (spherical) angle (measuring east) that $J$ makes with the vernal equinox.

It ranges from $0$ to $360 \degrees$.

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