erfc function usage in Vensim

[usmk]

Hi,

I am working with groundwater contamination and am trying to put together a model for this, which implements the complementary error function (erfc). This function is not offered in Vensim. In excel, the work-around would be to use a statistical function called NORMSDIST. But this function is also not available in Vensim. I am now thinking maybe the only solution is to use a LOOKUP function, and manually draw the erfc curve. Is this the best way to go? Or are there any other possibilities (i.e. plugins or something I might not know about)?

Many thanks in advance,
Ursula

[tomfid]

Here's a macro that implements the cumulative normal: http://models.metasd.com/cumulative-nor ... tribution/ ERF & ERFC are a simple transformation from there. The lookup approach also works OK for most purposes.

[usmk]

I forgot to say thanks for the help! It seems to be working fine as a Lookup curve...I am still planning to try out the macro solution anyway though.

USMK