===== Cauchy principal value =====
==== Partial function ====
| @#FFBB00: definiendum | @#FFBB00: $\mathcal P\int_a^b: \mathbb R^2\times(\mathbb R\to\overline{\mathbb R})\to\overline{\mathbb R}$ |

| @#BBDDEE: $p$ ... ordered sequence of the $m$ poles of $f$  |

| @#FFBB00: definiendum | @#FFBB00: $\mathcal P\int_a^b(f):=\mathrm{lim}_{\varepsilon\to 0}\left(\int_a^{p_1-\varepsilon}f(x)\,\mathrm dx+\int_{p_1+\varepsilon}^{p_2-\varepsilon}f(x)\,\mathrm dx+\cdots+\int_{p_m+\varepsilon}^b f(x)\,\mathrm dx\right)$ |

==== Discussion ====
The Cauchy principal value is the value of an integral where the singularities are approached in a //symmetric// fashion.

=== Examples ===
$\mathcal P\int_{-3}^7\left(\lambda x.\frac{1}{x}\right)=\int_{-3}^{-\varepsilon}\frac{1}{x}\,\mathrm dx+\int_{\varepsilon}^{7}\frac{1}{x}\,\mathrm dx=\left(\log\left|-\varepsilon\right|-\log\left|-3\right|\right)+\left(\log\left|7\right|-\log\left|\varepsilon\right|\right)=\log\left|\frac{7}{3}\right|$
=== Reference ===
Wikipedia: [[http://en.wikipedia.org/wiki/Cauchy_principal_value|Cauchy principal value]]
==== Parents ====
=== Requirements ===
[[Lebesgue measure]]
=== Related ===
[[Pole of a complex function]]