MaplePrimes - answers and comments on Question, Add further elements to a previously created array?

Array

acer — Tue, 16 Feb 2010 18:57:20 Z

Note that below I use an Array (capitalized).

> X:=Array(3): # originally with 3 elements only

> for i from 1 to 5 do
>  X(i):=i^2;
> end do:

> X; # using Maple 13, X can be "grown" to be of length 5
                        [1 4 9 16 25]

In much older versions of Maple, I would not have been able to grow X in size, and would have been limited to its original 3 entry spots. And I would have had to use the syntax X[i]:=... instead of X(i):=...

I could also have used a table structure, which is yet another type of mutable structure with an open-ended number of entries.

Note also that X was not created using X:=[...] as that would have created a list rather than an Array. See here for a bit more about comparison between Maple's data structures.

acer

Hi, sorry I did mean a list

plummie — Wed, 17 Feb 2010 03:49:29 Z

Hi, sorry I did mean a list not an array. (It was easier to do it that way)

I managed to figure it out, in case anyone else is interested I used
N:=[op(N),a] to add a onto my list of elements.

Thankyou for your help though.

can you increase the size of an array

Christopher2222 — Wed, 17 Feb 2010 22:18:30 Z

Can you increase the size of array or Matrix without changing it's contents? I seem to recall reading something somewhere in the last two weeks on this exact topic, I am unable to find it. Is there a way?

expansion

Christopher2222 — Sat, 27 Feb 2010 07:20:07 Z

ooops yes, scanned it too quickly. Thanks yes the maple 12 page was exactly where I saw it.

a:=Matrix([m1,m2,m3,m4]);

[m1,m2,m3,m4]

a(1,9):=m9:
a;
[ m1 , m2 , m3 , m4 , 0 , 0 , 0 , 0 , m9 ]

To better reference the location with some nice examples. It is located here, linked from the page that was referenced: http://www.maplesoft.com/support/help/AddOns/view.aspx?path=rtable_indexing with the heading indexing Arrays, Matricies, and Vectors.

The maple help system is a little broken up and segmented, sometimes the answer is burried deep into an unknown category totally unrelated and sometimes never in a location you might think it should be. Just one of the interesting and sometimes hairpulling quirks in Maple... "hmm now where did I see that example again?" I've had that happen actually a number of times and not always easy to find my answer, sometimes Mapleprimes is the best and fastest way to get the answer.

Inefficient

Robert Israel — Wed, 17 Feb 2010 04:21:39 Z

That does work, but it is inefficient, because the whole list must be recreated to add one element. This may begin to get significant when the number of elements gets into the thousands. For example:

> ti:= time():
 A:= <1>:
 for i from 2 to 30000 do A(i):= i end do:
 time()-ti;

     .032

> ti:= time():
 L:= [1]:
 for i from 2 to 30000 do L:= [op(L),i] end do:
 time()-ti;

    10.967

Building an Array of size 30000 by adding one element at a time took only .032 seconds on my machine. The same thing with a list took 10.967 seconds.

which is a shame

acer — Wed, 17 Feb 2010 04:27:56 Z

And that is a shame, because as far as efficiency goes you've almost certainly chosen a suboptimal structure and method. Every time you add an element you create a new list, which involves overhead for creation, possibly simultaneous storage, and eventual garbage collection (memory management). For example, it can make a task that optimally uses linear storage have quadratic memory use, with potential for worse effects in performance due to memory management needs. It is perhaps one of the more famous of less desirable programming techniques (in Maple).

acer