From: Christopher Cullen (c.cullen@nri.org.uk)
Date: Sat Jan 10 2004 - 13:06:31 EST
The earliest statement on this point is that of Liu Hui 劉徽 around AD
263, who says:
正筭赤負筭黑否則以邪正為異
(Jiu zhang suan shu, chapter 8 p. 175 in Guo & Liu (eds) Suan jing shi
shu, Taibei 2001.)
Which means that the positive rods are red and the negative black, but
adds that when this is not the case (presumably because one does not
have coloured rods) "one makes a difference by means of the inclined
and straight". No further explanation is given in Liu Hui's text, but
In later practice (as evidenced in the 13th C.) this appears to have
meant that one set out the number as usual, but with an extra rod laid
diagonally across the right-hand numeral of a given number. I do not
recall having heard of any excavated sets of counting-rods showing
signs of having been coloured, but I have not checked this.
For completeness, perhaps one should also ask for the encoding of a set
of "diagonally cancelled" rod numerals so that the second style for
negative numbers could be represented.
Christopher Cullen
On 10 Jan 2004, at 15:25, Elliotte Rusty Harold wrote:
> One very interesting thing I noted on the page:
>
> Negative numbers were usually represented using distinguisable
> features like color. Positive rods were usually colored red while
> negative rods were usually colored black.
>
> Wasn't there a really long thread not very long ago about whether
> color was ever a distinguishing characteristic of two otherwise
> identical characters?
> --
>
> Elliotte Rusty Harold
> elharo@metalab.unc.edu
> Effective XML (Addison-Wesley, 2003)
> http://www.cafeconleche.org/books/effectivexml
> http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/
> cafeaulaitA
>
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