# Missing $inserted (multicolumn) \multirow{2}{*}{Part} & \multicolumn{2}{|c|}{\sigma_{I}} & \multicolumn{2}{|c|}{\sigma_{II}} \\ \cline{2-5}  I am compiling this code, I am getting the error Missing$ inserted and after that it is giving me the desired result. But still I dont wan't any errors in my code.

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Welcome to TeX.SX! –  egreg Nov 29 '12 at 15:04

Presumably (you could have said) you are in a tabular rather than an array so it defaults to text mode so to get a sigma you need
 \multicolumn{2}{|c|}{$\sigma_{I}$}