Hello all, I have another question for the experts where I did not find any answer, yet. It's about the shape parameter of the gamma distribution of rate variation. Known as Alpha. I know what the parameter is, and I know that if when Alpha = 1 the gamma distribution matches the exponential distribution. My question is: What does the setting "exponential" for example at MrBayes mean? At MrBayes I can set Shapepr=exponential(value). And I can set Shapepr=fixed(value). What is the difference? All the best Dieter
Hi Dieter, from what I understand, the use of exponential means that the tested gamma distributions become virtually infinite, as it would then be based on an exponential range of α (alpha). I think that the value that's passed to
Exponential may relate to λ (lambda).
The other options for
- uniform (the default, I believe), α values between 0 and 1.0 are tested
- fixed, fixed at a specific value of α
You may wish to confirm with the author of MrBayes.