Published online by Cambridge University Press: 20 November 2018
We will give a representation-theoretic proof for the multiplication formula in the Ringel-Hall algebra   $\mathfrak{H}\vartriangle \,(n)$  of a cyclic quiver
 $\mathfrak{H}\vartriangle \,(n)$  of a cyclic quiver   $\Delta \,(n)$ . As a first application, we see immediately the existence of Hall polynomials for cyclic quivers, a fact established by J. Y. Guo and C. M. Ringel, and derive a recursive formula to compute them. We will further use the formula and the construction of a monomial basis for
 $\Delta \,(n)$ . As a first application, we see immediately the existence of Hall polynomials for cyclic quivers, a fact established by J. Y. Guo and C. M. Ringel, and derive a recursive formula to compute them. We will further use the formula and the construction of a monomial basis for   $\mathfrak{H}\vartriangle \,(n)$  given by Deng, Du, and Xiao together with the double Ringel-Hall algebra realisation of the quantum loop algebra
 $\mathfrak{H}\vartriangle \,(n)$  given by Deng, Du, and Xiao together with the double Ringel-Hall algebra realisation of the quantum loop algebra   ${{U}_{v}}({{\widehat{\mathfrak{g}\mathfrak{l}}}_{n}})$  given by Deng, Du, and Fu to develop some algorithms and to compute the canonical basis for
 ${{U}_{v}}({{\widehat{\mathfrak{g}\mathfrak{l}}}_{n}})$  given by Deng, Du, and Fu to develop some algorithms and to compute the canonical basis for   $U_{v}^{+}({{\widehat{\mathfrak{g}\mathfrak{l}}}_{n}})$ . As examples, we will show explicitly the part of the canonical basis associated with modules of Lowey length at most 2 for the quantum group
 $U_{v}^{+}({{\widehat{\mathfrak{g}\mathfrak{l}}}_{n}})$ . As examples, we will show explicitly the part of the canonical basis associated with modules of Lowey length at most 2 for the quantum group   ${{U}_{v}}({{\widehat{\mathfrak{g}\mathfrak{l}}}_{2}})$ .
 ${{U}_{v}}({{\widehat{\mathfrak{g}\mathfrak{l}}}_{2}})$ .
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