Recently, I am fluent in studying UDF, and some don't know much about it, NV _ vs (); c _ UDSI _ G()； C_UDSI_DIFF (), what do these commands mean? Thank you.

Just some macros, which can simplify the operation.

Sets the value of a vector (array) with the result of scalar operation.

C_UDSI_G () takes the gradient of the unit UDS variable.

C_UDSI_DIFF takes the difference of the unit UDS variable.