Clenshaw–Curtis quadrature

Clenshaw–Curtis quadrature and Fejér quadrature are methods for numerical integration, or "quadrature", that are based on an expansion of the integrand in terms of Chebyshev polynomials. Equivalently, they employ a change of variables x = cos ⁡ θ {\displaystyle x=\cos \theta } and use a discrete cosine transform (DCT) approximation for the cosine series.