Takes GM values and transforms them to AR1

gm_to_ar1(theta, freq)

## Arguments

theta

A vec that contains AR1 values.

freq

A double indicating the frequency of the data.

## Value

A vec containing GM values.

## Author

James Balamuta The function takes a vector of GM values $$\beta$$ and $$\sigma ^2_{gm}$$ and transforms them to AR1 values $$\phi$$ and $$\sigma ^2$$ using the formulas: $$\phi = \exp \left( { - \beta \Delta t} \right)$$ $${\sigma ^2} = \sigma _{gm}^2\left( {1 - \exp \left( { - 2\beta \Delta t} \right)} \right)$$