# FRESNELC

## Purpose:

Evaluates the Fresnel Cosine Integral.

## Syntax:

FRESNELC(x, xc)

 x - A real or series, the integration limit. xc - Optional. A real, the cutoff limit that determines the integration limit. Defaults to 1.8.

## Returns:

A scalar or series, the value of C(x), the integration of cos(πt2/2) from 0 to x.

## Example:

fresnelc(1)

returns 0.779893 the value of:

## Example:

fresnelc({0.1, 0.2, 1, 2})

returns {0.099998, 0.199921, 0.779893, 0.488253}, the value of the integral with limits {0.1, 0.2, 1, 2}.

## Example:

fresnelc(-5..0.01..5);

xlabel("x");ylabel("C(x)");label("Cosine Fresnel");

returns 1001 samples of the Fresnel Cosine Integral with integration limits from –5 to 5.

## Remarks:

The Fresnel Cosine Integral, C(x), is defined as:

For abs(x) < xc, a power series about x = 0 is used yielding an accuracy better than 5e-16.

For abs(x) > xc, a minimax rational approximation based on auxilliary functions described in [1] is used yielding an accuracy better than 1e-9.

See FRESNELS to evaluate the sine form of the Fresnel integral.

FRESNELC was developed from an algorithm by J. N. McElwaine.

COSINT

ERF

FRESNELS

GAMMA

GAMMALN

## References:

[1]   Abramowitz and Stegun

Handbook of Mathematical Functions (9th printing 1970)

US Gov. Printing Office

Section 7.3 p300