Paul, Thank you so much for your valuable advice. In fact this seems to be the only way to handle many equations at the same time. One of my colleagues gave me this idea which also works fine:
1) Export from LyX to dvi (say eq0.dvi) 2)in the command prompt write: dvips -E -o eq0.eps eq0.dvi you get the eps file with the correct bounding box. Mukhtar
