[Matrix-SIG] Active arrays

[Bryce Gardner]

>-- Then some names for this `active' thingy.
>
>>typed
>>keeptype
>>hold
>>holdtype
>
>How about 'promote', set to '0' if promotion to double is not wanted?

I was thinking 'dominant_type' because we want this type to attempt to
control the
final type of an expression.  Something that lends the idea that this type
is intended 
to control the type of the output.  

Some other words could be overriding_type, prevailing_type, principal_type.

just my two-cents worth.

Bryce