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In this paper, we develop an accurate pseudospectral method to approximatenumerically the Riesz-Feller operator $D_\gamma^\alpha$ on $\mathbb R$, where$\alpha\in(0,2)$, and $|\gamma|\le\min\{\alpha, 2 - \alpha\}$. This operatorcan be written as a linear combination of the Weyl-Marchaud derivatives$\mathcal{D}^{\alpha}$ and $\overline{\mathcal{D}^\alpha}$, when$\alpha\in(0,1)$, and of $\partial_x\mathcal{D}^{\alpha-1}$ and$\partial_x\overline{\mathcal{D}^{\alpha-1}}$, when $\alpha\in(1,2)$.  Given the so-called Higgins functions $\lambda_k(x) = ((ix-1)/(ix+1))^k$,where $k\in\mathbb Z$, we compute explicitly, using complex variabletechniques, $\mathcal{D}^{\alpha}[\lambda_k](x)$,$\overline{\mathcal{D}^\alpha}[\lambda_k](x)$,$\partial_x\mathcal{D}^{\alpha-1}[\lambda_k](x)$,$\partial_x\overline{\mathcal{D}^{\alpha-1}}[\lambda_k](x)$ and$D_\gamma^\alpha[\lambda_k](x)$, in terms of the Gaussian hypergeometricfunction ${}_2F_1$, and relate these results to previous ones for thefractional Laplacian. This enables us to approximate$\mathcal{D}^{\alpha}[u](x)$, $\overline{\mathcal{D}^\alpha}[u](x)$,$\partial_x\mathcal{D}^{\alpha-1}[u](x)$,$\partial_x\overline{\mathcal{D}^{\alpha-1}}[u](x)$ and$D_\gamma^\alpha[u](x)$, for bounded continuous functions $u(x)$. Finally, wesimulate a nonlinear Riesz-Feller fractional diffusion equation, characterizedby having front propagating solutions whose speed grows exponentially in time.

Numerical Approximation of Riesz-Feller Operators on $\mathbb R$