SampleUtils::someff Namespace Reference

Description

Some form factor functions.

Functions
complex_t	ffSphere (C3 q, double R)
	Returns the form factor of a sphere of radius R. More...

Function Documentation

ffSphere()

complex_t SampleUtils::someff::ffSphere	(	C3	q,
		double	R
	)

Returns the form factor of a sphere of radius R.

Used by the hard sphere and by several soft sphere classes.

Definition at line 21 of file SomeFormFactors.cpp.

{
    complex_t q1 =
        sqrt(q.x() * q.x() + q.y() * q.y() + q.z() * q.z()); // NO sesquilinear dot product!
    complex_t qR = q1 * R;
 
    if (std::abs(qR) < 1e-4) { // relative error is O(qR^4) with small prefactor
        // expand sin(qR)-qR*cos(qR) up to qR^5
        return 4 * M_PI / 3 * pow(R, 3) * (1. - 0.1 * pow(qR, 2));
    }
    return 4 * M_PI * pow(q1, -3) * (sin(qR) - qR * cos(qR));
}

References M_PI, and TMath::R().

Referenced by Sphere::formfactor_at_bottom(), and FuzzySphere::formfactor_at_bottom().

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