# Thread: Even/Odd detection formula for use in families

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## Even/Odd detection formula for use in families

Hi All,

I don't know if this has been done or not, or indeed if anyone else has ever wanted such a thing...

I have created a one-line formula that provides a boolean test (yes/no) of whether an input value is even or odd, for values greater than 1.

Create two parameters - one is the value you want to test. This must be an integer, so use either the integer class or use round(x) on another value. Let's use a parameter type integer, and call it TEST.

The second parameter is your boolean (yes/no) - call the parameter EVEN

Insert this formula in the formula field for the EVEN parameter:

Code:
`(rounddown(TEST / 2)) - (rounddown((TEST - 1) / 2)) > 0`
If the value of TEST is an even number, EVEN will be TRUE (ticked/yes); if TEST is an odd number, EVEN will be FALSE (unticked/no).

Where this might be useful:

I have used this in parametric door families for folder doors, to provide a boolean value to display the fixed leaf if an odd number of doors is used. I have also used it in shelving systems to allow a blank panel to appear when the shelves are odd. You might have some other uses for it.

Note that this will produce erratic results if provided with negative numbers, 0 or 1 as an input. This can be avoided through use of clever IF statements, and is left as an exercise for the reader.

How it works:

The formula tests the difference between a given value X/2 and (X-1)/2, with both values rounded down before the difference is performed. For an example value of 3 the equation is thus:

Code:
```Input values:  (3/2)  - (3-1/2) = (3/2)  -  (2/2)

Result values:   (1.5)  -  (1)

Rounded Down:   (1)  -  (1)  = 0 THEREFORE X is ODD where X=3```

For an example value of 42:

Code:
```Input values:  (42/2)  - (42-1/2) = (42/2)  -  (41/2)

Result values:   (21)  -  (20.5)

Rounded Down:   (21)  -  (20)  = 1 THEREFORE X is EVEN where X=42```

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## Re: Even/Odd detection formula for use in families

Clever! Have to keep this one around!

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## Re: Even/Odd detection formula for use in families

i remember an AU webinar from c2009 called something like fuzzy math for revit that had another rounding solution. yours seems simpler though. nice work!

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## Re: Even/Odd detection formula for use in families

http://aucache.autodesk.com/au2008/s...-1-Handout.pdf

heres the course handout. I guess it was AU08. the video was pretty interesting.

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## Re: Even/Odd detection formula for use in families

You made my folding door, odd-even panel number finally work in a simple way
I wish I could buy you a drink as thank you.
Just made my day (a sad life of a BIM manager when this stuff makes his day)

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