CoCoA » CoCoALib

We could introduce a flag to say whether to print spaces between summands in polynomials.

The flag could be compile time or run-time. Since great speed is not crucial, there is no real advantage to using a compile-time flag. A run-time flag could even be user settable (perhaps belonging to the GlobalManager?).

Addendum removing the space before the + or - sign is very simple (just disable line 529 in SparsePolyRing.C); adding a space after the + sign is simple too (change lines 530 and 552), but adding a space after the - sign is more tricky because the - sign is printed as part of the coefficient. Unfortunately the documentation for IsPrintedWithMinus (in the doc for RingElem) is not as clear as I would like.

John Abbott wrote:

The flag could be compile time or run-time. Since great speed is not crucial, there is no real advantage to using a compile-time flag. A run-time flag could even be user settable (perhaps belonging to the GlobalManager?).

I agree

Addendum removing the space before the + or - sign is very simple (just disable line 529 in SparsePolyRing.C); adding a space after the + sign is simple too (change lines 530 and 552), but adding a space after the - sign is more tricky because the - sign is printed as part of the coefficient. Unfortunately the documentation for IsPrintedWithMinus (in the doc for RingElem) is not as clear as I would like.

If my memory works well the reason why there is no space after the sign came originally from the fact that "-2" (int) is printed like that.
Then I saw (and I'm still convinced) that it's more compact, while nicely separating the summands in a polynomial).

To add the space after "-" we would probably only need to intercept the printing of negative machine integers and print "- " and the absolute value.

CoCoA-4 printed like this (no space for the first term).
What to do?

-3x - 1

Christof and John looked at various possible printed forms of (3-2*x)^5

[a]  -32*x^5+240*x^4-720*x^3+1080*x^2-810*x+243
[b]  -32*x^5 +240*x^4 -720*x^3 +1080*x^2 -810*x +243
[c]  -32*x^5 + 240*x^4 - 720*x^3 + 1080*x^2 - 810*x + 243
[d]  - 32*x^5 + 240*x^4 - 720*x^3 + 1080*x^2 - 810*x + 243

We also looked at the polynomial (2*a-x)^5 in the ring QQ[a][x]

[aa]  -x^5 +(10*a)*x^4 +(-40*a^2)*x^3 +(80*a^3)*x^2 +(-80*a^4)*x +32*a^5
[bb]  -x^5 + (10*a)*x^4 + (-40*a^2)*x^3 + (80*a^3)*x^2 + (-80*a^4)*x + 32*a^5
[cc]  -x^5 + (10*a)*x^4 - (40*a^2)*x^3 + (80*a^3)*x^2 - (80*a^4)*x + 32*a^5
[dd]  -x^5 + 10*a*x^4 - 40*a^2*x^3 + 80*a^3*x^2 - 80*a^4*x + 32*a^5

ADDENDUM JAA notices that the final term 32*a^5 was not printed in brackets. Why not?

JAA proposes the following guideline:

• the coefficients +1 and -1 are handled specially, or
• the coefficient is an integer (i.e. IsInteger gives true), or
• the power product is 1 and the coefficient is rational (i.e. IsRational gives true)
• negative integer/rational coefficients are handled specially (i.e. not ...+(-c)*x^k)

Here are some examples:

[A] x^2 - 1   // any ring
[B] x^2 - 1/4 // any ring, special handling for negative rational
[C] x^2 + (-1/4) // any ring
[D] x^2 - a          // element of QQ[a,x]
[E] x^2 - (1/4)*a    // element of QQ[a,x], special handling for negative rational
[F] x^2 + (-1/4)*a   // element of QQ[a,x]
[G] x^2 + (-a)       // element of QQ[a][x]
[H] x^2 + ((-1/4)*a) // element of QQ[a][x]
[I] x^2 + (-(1/4)*a) // element of QQ[a][x], special handling for negative rational
[J] x^2 - (1/2)*x + 1/16  // any ring, no brackets around 1/16, special handling for -1/2
[K] x^2 + (-1/2)*x + 1/16
[L] x^2 + (-1/2)*x + (1/16)

Opinions about [B] versus [C]?
Opinions about [E] versus [F]?
Opinions about [J] versus [K] versus [L]?
Any other opinions/suggestions/examples?

2013-02-18 JAA thinks [C] is ugly. JAA mildly prefers [E] to [F], but incompatibly also thinks that [H] is nicer than [I]. Aesthetically [K] looks nicer than [L], but [L] is more uniform.

I would prefer a symmetric appearance, either no space around the + sign or a blank on bothsides.

But it is a matter of taste and adaptation --- if one has seen the asymmetric apperance long enough one gets used to it.

I notice in SparsePolyRing.C:551 that there is a check via IsPrintAtom. The documentation says true iff arg does not need brackets when a num or denom of a fraction

So how should x^2 - x/a - 1/a (elem of QQ(a)[x]) be printed?

[aaa] x^2 + (-1/a)*x + (-1/a)
[bbb] x^2 - (1/a)*x - (1/a)
[ccc] x^2 - (1/a)*x - 1/a

Idle for more than 6 years: perhaps because there is no clear answer, and implementation might be tricky :-/

SOURCE CODE has moved: now near SparsePolyOps-RingElem.C:480

THIS REPLY BASED ON MY MISTAKE IN COMMENT 19
On my computer I get

/**/ FF7a ::= ZZ/(7)[a];
/**/ use P ::= FF7a[x];
/**/ (x-2)^3;
x^3 +x^2 -2*x -1

I think I am missing something in your proposal.
I believe we should close this issue (originated for deciding spaces around signs) and make new ones, more specific.

Sorry I typed in the example wrongly: there should have been a quotient (now corrected -- see comment 19)