Hello Andrey,
(back from vacation

)
I tried some differentiation on the function of vector (matrix) argument. As we know, Mathcad does not allow this (I do not know for the version 14). Here is the first picture (recent SMath 0.82)

Please see what the symbolic answer gives - the same results? Here might be some logic to represent this as the differentiation of product of complex functions. The numerical differentiation will report "Assign variable" error.
Here is another picture. Here the x vector is given with a and b not defined before. See the result.

Quite strange? The firts two results are the same. Could not understand this.
Any comments?
Regards,
Radovan
When Sisyphus climbed to the top of a hill, they said: "Wrong boulder!"