Well, positiveRemainder should be renamed "mod". Also, addmod, submod,
mulmod assume that their first two parameters are positive, which is an
unreasonable restriction. For example:
(1) -> addmod(-13,0,10)
(1) - 13
(2) -> mulmod(-13,1,10)
(2) - 3
(3) -> submod(-13,0,10)
(3) - 3
(4) -> submod(0,13,10)
(4) -3
In fact, there should be two mod commands: x mod n, which produces a result
between 0 and n-1, and x bmod n (for "balanced mod") which produces a result
between -(n-1)/2 and (n-1)/2 if n is odd, and between -(n-2)/2 and n/2 if n
is even.
Looking through si.spad, it could easily be extended by
x mod y == MOD(x,y)$Lisp::INT
or some such.
cheers,
Alasdair
On 7/11/07, Bill Page <[EMAIL PROTECTED]> wrote:
On 7/10/07, Alasdair McAndrew wrote:
> Yes, that's pretty much what I did. But surely such an important
function
> as mod should be available without having to write it yourself?
> ...
Digging a little deeper I found in the domain 'Integer':
(1) -> positiveRemainder(-13,10)
(1) 7
Type: PositiveInteger
I presume this is what you were looking for?
Also take a look at
(2) -> addmod(13,1,10)
(2) 4
Type: PositiveInteger
(3) -> submod(13,1,10)
(3) 12
Type: PositiveInteger
(4) -> mulmod(13,2,10)
(4) 6
Type: PositiveInteger
Regards,
Bill Page.
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