Matrix issue PTC Mathcad 10.0.1.0

OK, in the meantime you already know that the problem was that you defined x as a range and not as a vector.

Instead of using an extra variable i to index the vector to create or to use a utility function to turn a range into a vector, you could also use a utility function which created the vector right ahead - similar to a range definition by providing the first, second and end value.

Furthermore it makes not much sense to me that you strip the unit feet when defining the range/vector "x" just to add the unit again when using "x" in the definition of V.ADL. You don't have to strip the units when defining a range or a vector.

In case of this simply calculation it would not have been necessary to use vectorization (the arrow over the expression). But its good style and I would suggest to always use it when applying a scalar calculation to vector arguments.

If D would be a vector as well, vectorization would be absolutely necessary as otherwise the multiplication would be done as dot-product (scalar product) and the result so would be a single value and not a vector with 6 values.

BTW, what you did  - following the definition of the range immediately by an evaluation (the = sign at the end) - automatically turned the range into a vector in older Prime versions. So what you did would work without problems in versions of Prime up to P9. Prime 10 is the first version where this undocumented trick does not work anymore. That's the reason you have to resort to other methods to define x as a vector. Three methods to do so where shown in this thread. PTC promised to provide a easier built-in way (either to turn a range into a vector or to create a vector similar to a range, I don't know) in Prime 11.

Prime 10 sheet attached