Make initial guessing consistent in terms of (initial, final) value pairs or (initial, duration)

Desired capability or behavior.

Migrated from old repo:

"I thought that, for initial guesses on dymos phases, we provide an initial and final value. Here it looks like an initial value and a delta, which is a little inconsistent."

Originally posted by @Kenneth-T-Moore

John's response: I agree with you it's a bit inconsistent. This is true because Dymos is expecting initial-final pairs for some things and initial-duration pairs for others (like time or in this case, mass). We can remove that complexity from an Aviary user though with some quick math. I'll make an issue based on your comment for this.

This will be a breaking non-backwards-compatible change, must increment version accordingly.

Is your feature request related to a problem? Please describe.

No response

Associated Bug Report

No response