This function converts a transformation name to the corresponding function. Convertion is from original scale to real scale by default. Available transformations:
exp4: $(4x)$, inverse is $(x)/4$exp2: $(2x)$, inverse is $(x)/2$tanh: Hyperbolic tangent transformation used for AR1 parameter, uses ar1_th2a and ar1_a2thidentity: Identity function, no transformationexp: $(x)$, inverse is $(x)$sqrt: $(x)$, inverse is $x^2$square: $x^2$, inverse is $(x)$log: $(x)$, inverse is $(x)$