====== Boolean Masks ======

Boolean masks are often used to 'filter' the values of arrays, based on some logical criteria (e.g. negative or positive values). Using a mask is a two-step process: 
  - Creation of the mask using boolean operator(s) (e.g. greater than, less than or equal to)
  - Application of the mask to some array to be filtered, simply by multiplication.

==== Example ====

Starting with this TOOL object ''newDwellings[dt,t]''

{{:recipies:examplebooleanmask1.png|}}

the mask is created with this code

<code>
maskPositive[dt,t] = boolge (newDwellings[dt,t], 0)
</code>

{{:recipies:examplebooleanmask3.png|}}

and applied

<code>
newDwellingsPos[dt,t] = newDwellings[dt,t] * maskPositive[dt,t]
</code>

to produce 

{{:recipies:examplebooleanmask2.png|}}

Note that the mask can be easily inverted by subtracting it from one

<code>
maskNegative[dt,t] = 1 - maskPositive[dt,t]
</code>

{{:recipies:examplebooleanmask4.png|}}

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{{:recipies:examplebooleanmask.t|}} is the self-contained TOOL script for this example.