Error when trying to sum two products, where one product is a 1x2 matrix

Question

First question that I've posted here, I'm working on some code for my final on Monday and for some reason I keep getting the following error. Any help would be MASSIVELY appreciated. Thanks!;

The following imagine shows the error in my code, I had switched to 1D math and still can't seem to find the issue

Answer 1

In Maple the global name D has a preassigned value. It is the differential operator. For example,

f := t -> sec(t):

D(f);

      t -> sec(t)*tan(t)

The global name D is also protected, ie. you cannot assign another values to it.

And in general it is not a good idea to use the name D like a dummy variable in your code (since is has already been assigned a system procedure, by default). Your example is an (unfortunate) example of strangeness that could ensue.

D * Vector([-3,1]);
  Error, (in LinearAlgebra:-Multiply) invalid arguments

You have a couple of alternatives:

1) Use another name instead, such as DD.

2) If you Maple version is recent then you could declare it (once) as a local name for top-level use. For example,

restart;

local D;

               D

D * Vector([-3,1]);

             [-3 D]
             [    ]
             [ D  ]

If you do declare local D for top-level use then you can still utilize the differential operator by its global name :-D. Eg.

restart;
local D:

f := t -> sec(t):

D(f);     # does nothing, since this is the local D

             D(f)

:-D(f);

       t -> sec(t)*tan(t)

If all that sounds confusing, you'll probably be better off just using another name instead.

The are only a few short symbols with preassigned values or uses, eg. Pi, I, D.

You might want to also have a look at the Help page for Topics initialconstants and trydeclaringlocal .