MaplePrimes - answers and comments on Question, how to compare whether two lists are equal

immutable

roman_pearce — Wed, 24 Feb 2010 06:21:40 Z

Lists and polynomials are immutable in Maple (changing them makes an entirely new object) so you can just use = to test. For example:


A := [x^2+x+1,x-1];
B := [x^2+x+1,x-1];
evalb(A=B);

thanks. Another question: if

gepo — Wed, 24 Feb 2010 06:49:51 Z

thanks. Another question: if they are different, can I see the differences? A:=[x^2+x+1,x-1]; B:=[x^2+x+1]; how can I compute A-B? Thanks Gepo

define difference of lists

Joe Riel — Wed, 24 Feb 2010 10:01:57 Z

You need to define what you mean by the difference of two lists. Giving the expected output for the following may suffice,

listdiff( [1,2,2,3,3], [2,1] );

Possible answers are 
 1. error (lists must be the same size)
 2. [-1,1,2,3,3] (difference of corresponding elements, augmented with zero)
 3. [2,3,3] (multiset difference)
 4. [3,3]   (erasure?)

not entirely true

pagan — Wed, 24 Feb 2010 06:40:52 Z

As stated, that is not accurate.

We may have reason to suspect that the OP is considering exact rational coefficients for the polynomials due to some earlier posts. But evalb may not be adequate for testing polynomials with coefficients in the float domain.

> A := [a^2+b+1,a-1.00]:
> B := [a^2+b+1,a-1.0]:

> evalb(A=B);
                                     false
 
> verify(A,B,list('polynom'(float(10),{a,b})));
                                     true

With floats in the picture, it's up to the individual to decide what is accepted as "equal".

> evalb(1.0=1.00);
                                     true
 
> evalb(a-1.0=a-1.00);
                                     false

difference of lists

Robert Israel — Wed, 24 Feb 2010 08:59:40 Z

If the lists have the same length, you can simply subtract:

> A-B;

If not, you can use

> zip(`-`, A, B, 0);

which will pad the shorter one with 0's.