Centre

(idea) by Noether Tue Aug 08 2000 at 13:39:53
The centre (or center) of a ring R is the subring of elements that commute with all other elements
Z(R)={z in R such that zr=rz for all r in R}.

Elements in the centre are called central. (The letter Z here is coming from the German zentrum.)

Examples

There is a similar notion of centre for groups.

(definition) by Webster 1913 Tue Dec 21 1999 at 22:24:40

Cen"ter, Cen"tre v. i. [imp. & p. p. Centered or Centred (&?;); p. pr. & vb. n. Centering or Centring.]

1.

To be placed in a center; to be central.

2.

To be collected to a point; to be concentrated; to rest on, or gather about, as a center.

Where there is no visible truth wherein to center, error is as wide as men's fancies.
Dr. H. More.

Our hopes must center in ourselves alone.
Dryden.

 

© Webster 1913


Cen"ter , Cen"tre (?), v. t.

1.

To place or fix in the center or on a central point. Milton.

2.

To collect to a point; to concentrate.

Thy joys are centered all in me alone.
Prior.

3. (Mech.)

To form a recess or indentation for the reception of a center.

 

© Webster 1913


Cen"tre (?), n. & v.

See Center.

 

© Webster 1913


Cen"ter, or Cen"tre, seal . (Gas Manuf.)

A compound hydraulic valve for regulating the passage of the gas through a set of purifiers so as to cut out each one in turn for the renewal of the lime.

 

© Webster 1913


Center, or Centre, punch . (Mech.)

(a)

A punch for making indentations or dots in a piece of work, as for suspension between lathe centers, etc.

(b)

A punch for punching holes in sheet metal, having a small conical center to insure correct locating.

 

© Webster 1913

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