I'm wondering if there is an R package which can help me to get the correct parameters for a distribution of my choice and for intervals of my choice.

For Instance, here Betancourt is looking at inverse gamma and he wants to learn which set of parameters will give >1% below 2 and >1% above 20 (like the graph below). Stan's solver returns the parameters for inv-gamma which results the intervals of interest. Is there any solution applied directly on R?

Or in other words,

• I have the distribution
• I have the intervals

Can I learn the correct parameters?

Thanks