Method acos

src/main/java/field/linalg/BaseMath.java:35–55

Input-checking inverse cosine. Clamps the input to the domain of acos (i.e. [-1..1]) before evaluating, instead of returning a silent NaN like java.lang.Math.acos. Useful when there's a fear of rounding errors pushing the arg beyond 1 or -1.

(double cos_theta)

	 * fear of rounding errors pushing the arg beyond 1 or -1.
	 */
	public static final double acos(double cos_theta) {

		if (acos_lookup == null) {
			acos_lookup = new double[1000];
			for (int i = 0; i < acos_lookup.length; i++)
				acos_lookup[i] = Math.acos(clamp(-1.0 + 2 * i / (acos_lookup.length - 1f), -1, 1));
		}


		cos_theta = clamp(cos_theta, -1, 1);

		float indx = (float) ((acos_lookup.length - 1f) * (cos_theta + 1) / 2);
		int left = (int) indx;
		int right = (int) indx + 1;
		float alpha = indx - left;

		left = left < 0 ? 0 : (left > acos_lookup.length - 1 ? (acos_lookup.length - 1) : left);
		right = right < 0 ? 0 : (right > acos_lookup.length - 1 ? (acos_lookup.length - 1) : right);

		return acos_lookup[left] * (1 - alpha) + alpha * acos_lookup[right];
	}

	/**
	 * Input-checking inverse sine. Clamps the input to the domain of acos [-1..1] before evaluating, instead of returning a silent NaN like java.lang.Math.asin. Useful when there's a fear of