It was recently pointed out to me that the User Defined Function (UDF) for solving quartic polynomial equations presented in this post returned an error for some input values.  In tracking down the source of the error I decided that it would be useful to have a UDF that would evaluate a polynomial for complex roots, and in writing that I added some new functions to the ALGLIB complex number spreadsheet presented in this post.  The end result of this work is:

Three new functions for the AL-Complex spreadsheet (as always, all the spreadsheets mentioned here are available for download, including full open source code)

ALGLIB Complex number functions, click for full size view

A new complex number function for the EvalPoly spreadsheet:

EvalPoly spreadsheet

And corrected code for the Quartic function in the Polynomial Spreadsheet, plus evaluation of the maximum error in the input function using the roots generated by the Quartic and CubicC functions:

Quartic spreadsheet