Stata 15 help for _ms_op_info
[P] _ms_op_info -- Matrix stripe operator information
_ms_op_info returns an indication of whether matrix_name has factor
variables or time-series operators in any of its column stripe elements.
Factor variables include the omit operator, 'o', and interactions.
_ms_op_info stores the following in r():
r(fvops) indicator for factor variables
r(tsops) indicator for time-series operators