The common (base 10) logarithm of a complex number is calculated by the equation:
See Wikipedia for further information on complex numbers.The Excel Imlog10 function returns the common (base 10) logarithm of a supplied complex number.
The syntax of the function is:
where the inumber argument is the complex number that you want to find the base 10 logarithm of.
Note that complex numbers are simply stored as text in Excel. When a text string in the format "a+bi" or "a+bj" is supplied to one of Excel's builtin complex number functions, this is interpreted as a complex number.
Also the complex number functions can accept a simple numeric value, as this is equivalent to a complex number whose imaginary coefficient is equal to 0.
Therefore, the inumber argument can be supplied to the Excel Imlog10 function as any of the following:
The spreadsheets below show four examples of the Imlog10 function:
Formulas:
 Results:

Note that, in the above example spreadsheet:
Further details and examples of the Excel Imlog10 function are provided on the Microsoft Office website
If you get an error from the Excel Imlog10 Function, this is likely to be one of the following:
#NUM!    Occurs if the supplied inumber argument is not recognised as a complex number. 
#VALUE!    Occurs if the supplied inumber argument is a logical value. 