Dealing with v(end+1) when v(1) may not have been defined

I use the following kind of construction a lot

v(1) = (x+y)^2;
v(end+1) = (x^2 + 2*x*y + y^2)

etc. Sometimes v would be a vector of symbolic expressions, sometimes they are numeric.

I'd like to be able to initialize v in some way so that I could begin with

v(end+1) = (x+y)^2

and thus not treat the first element of the array in a special way.

I.e., I'd like to be able to do something like

v        = ''
v(end+1) = (x+y)^2;
v(end+1) = (x^2 + 2*x*y + y^2)

But this doesn't work. Is there a way to do this?

Thanks for any suggestions.

Answer 1

[Matt Fig]

v = [];
v(end+1) = 5;

Why would you want to do this, by the way?

[Leo Simon]

Thanks very much, Matt

Reason I do this: Often I define v(1) as some nasty symbolic expression computed by mupad, like simple(diff(some horrible expression)). Once I've got the expression I then simplify it down, keeping a record of my changes in a vector and checking periodically that the elements of the vector give the same answers for random values of the variables involved. Since mupad takes forever to do the computation I want to comment it out once I have the answer. But without your suggestion I'd have to redefine v(1). Now I can do:

      v = []
      v(end+1) = simple(diff(a mess))
      v(end+1) = <output from the diff command>
      v(end+1) = <simplification>

and simply comment out the mupad command once I have its answer.