S.Z.Exponential: Marginal survival function for the sum of two exponential...
In mbannick/survDeconvolution: Survival Deconvolution

If !correlated: X \sim Exponential(λ_{x}) \quad Y \sim Exponential(λ_{y})
If correlated: X \sim Exponential(λ_{x} \cdot k) \quad Y \sim Exponential(λ_{y} \cdot k) \quad K \sim Gamma(a, b)

1	S.Z.Exponential(t, a, b, parameters_x, parameters_y, correlated)

`t`	A number or vector, the survival times
`a`	A number, the shape parameter of Gamma frailty distribution
`b`	A number, the rate parameter of Gamma frailty distribution
`parameters_x`	A list, with an element named `lambda` (λ_x), the rate parameter of the exponential distribution
`parameters_y`	A list, with an element `lambda` (λ_y), the rate parameter of the exponential distribution
`correlated`	If TRUE, random variables that make up the sum are each conditionally exponential on the frailty parameter, that has Gamma(shape=a, rate=b) distribution.