smooth-gradient ("smg")
See this command in the command table.
To access this command:
- 
                                                    Surfaces ribbon >> String Tools >> Smooth Gradient. 
- 
                                                    Digitize ribbon >> Condition >> Condition >> Smooth Gradient. 
- 
                                                    Using the command line, enter "smooth-gradient" 
- 
                                                    Use the quick key combination "smg" 
- 
                                                    Display the Find Command screen, locate smooth-gradient and click Run. 
Command Overview
Smooth part of a string to a consistent gradient.
Select two separate points on a string. The elevations on all points between these two vertexes are adjusted so that each segment in this part of the string has the same gradient.

