NonConstants is an option for D which gives a list of objects to be taken to depend implicitly on the differentiation variables.
If c does not appear in the list of NonConstants, then D[
] is taken to be 0 unless c and x are identical expressions.
See the Mathematica book: Section 3.5.1.
See also: Dt.
Normally, if you differentiate a function with respect to x, say, Mathematica will treat all other parameters as constants.
By specifying that t depends upon x, you can get the desired result for such expressions.
THIS IS DOCUMENTATION FOR AN OBSOLETE PRODUCT.
SEE THE DOCUMENTATION CENTER
FOR THE LATEST INFORMATION.