how to enter erf(x) via formula node (string)?

[pauls]

I have Labview Professional package. Erf(x) is available as a functional block, but erf(x) is not recognized in formula node, or parsing the formula string.

[Dennis_Knutson]

This function is only available as a VI. While all of the formula node functions are available as a LabVIEW VI function, the opposite is not true.