Nudging

Positions of all labels may be adjusted, as can the amount of curvature for the curved arrows. The way this is done is by specifying a ``nudge'' factor ;SPMlt;num;SPMgt; at the beginning of the label. Here ;SPMlt;num;SPMgt; is a number which specifies the actual position of the label in units of |@| (the length of a single dash, normally 5pt) except with |.̇compositemap|, see below. Movement is constrained to the perpendicular bisector of the line #math453##tex2html_wrap_inline1746#. When nudging the label for the central Arrow it is the whole Arrow which is moved, along with its label.

Curvature of the arrows themselves is altered by a nudge of the form |.̇twocell|;SPMlt;num;SPMgt;.... The separation of the arrows, along the bisector, is set to be ;SPMlt;num;SPMgt;|@|. When ;SPMlt;num;SPMgt; is zero, that is |.̇twocell;SPMlt;0;SPMgt;...|, the result is a single straight arrow, its mid-point being the origin for nudging labels. A negative value for ;SPMlt;num;SPMgt; is also acceptable; but check the orientation on the Arrow and which of |^| and |_| correspond to which component.

The origin for nudging labels is where the arrow crosses the bisector. Positive nudges move the label outwards while negative nudges move towards #math454##tex2html_wrap_inline1748# and possibly beyond. The default position of a label is on the outside, with edge at the origin.

The origin for nudging the Arrow is at the midpoint of #math455##tex2html_wrap_inline1750#. A positive nudge moves in the clockwise direction. This will be the direction of the arrowhead, unless it has been reversed using |^|.

Labels on a |.̇compositemap| are placed relative to the midpoint of the component arrows. Nudges are in units of 1pt. Movement is in the usual -pic <#320#>above<#320#> and <#321#>below<#321#> directions, such that a positive nudge is always outside the triangle formed by the arrows and line #math456##tex2html_wrap_inline1752#.

The special nudge value |;SPMlt;;SPMgt;| typesets just the Arrow, omitting the curved arrows entirely. When used with labels, the nudge value |;SPMlt;;SPMgt;| causes the following label to be ignored.

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#exercise323#