I would like to use align environment over eqnarray for typesetting my equations. However the publisher forces to use the iopart.cls as the article class file which, as they mentioned, is incompatible with amsmath.sty.
How can I somehow import align definition (or even other definitions too) from amsmath.sty while sticking to the document class of iopart.cls ?

iopart.clshere and read through the manual and the.clsfile. It seems that the class file has its own definition ofeqnarray. For additional fonts, the manual says you have to write\usepackage{iopams}which will include the style files:amsgen,amsfonts,amssymb, andamsbsy, all version1995/01/01. Well, you can try\RequirePackage{amsmath}before\documentclassbut it will not give you the same indentation when usingiopart'seqnarray. I think there is a workaround but it's beyond my skills.:-)– hpesoj626 Jan 29 at 7:41iopartclass corrects the worst error ineqnarray. I'm afraid thatamsmathis "take or leave": extracting one of the environments requires getting also a great part of the auxiliary macros. For instance,amsmathredefines the equation numbering system. – egreg Jan 29 at 7:51amsmath, and suggested usingeqnarray. @ egreg: I didn't know theeqnarrayofiopartis the corrected version. If this is the case, it might be unnecessary for me to switch toalign! – M.Reza Jan 29 at 13:02