c) = c x^{-c-1} \exp(-x^{-c})

for :math:`x > 0`, :math:`c > 0`.

`invweibull` takes ``c`` as a shape parameter for :math:`c`.

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References
----------
F.R.S. de Gusmao, E.M.M Ortega and G.M. Cordeiro, "The generalized inverse
Weibull distribution", Stat. Papers, vol. 52, pp. 591-619, 2011.

%(example)s

c