Fresnel integral

The Fresnel integrals S(x) and C(x) are two transcendental functions named after Augustin-Jean Fresnel that are used in optics and are closely related to the error function (erf). They arise in the description of near-field Fresnel diffraction phenomena and are defined through the following integral representations:

$${\displaystyle S(x)=\int _{0}^{x}\sin \left(t^{2}\right)\,dt,\quad C(x)=\int _{0}^{x}\cos \left(t^{2}\right)\,dt.}$$

The parametric curve ⁠${\displaystyle {\bigl (}S(t),C(t){\bigr )}}$⁠ is the Euler spiral or clothoid, a curve whose curvature varies linearly with arclength.