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Davies, R. B. (1980). "Algorithm AS155: The distribution of a linear combination of χ2 random variables". Journal of the Royal Statistical Society. Series C (Applied Statistics). 29 (3): 323–333. doi:10.2307/2346911. JSTOR2346911.
Sheil, J.; O'Muircheartaigh, I. (1977). "Algorithm AS106: The distribution of non-negative quadratic forms in normal variables". Journal of the Royal Statistical Society. Series C (Applied Statistics). 26 (1): 92–98. doi:10.2307/2346884. JSTOR2346884.