I have two little problems with the alignment here:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{alignat*}{6}
\Phi \left(\sum\limits_{m\in M}r_m\delta _m + \sum\limits_{m\in M}r_m'\delta _m\right) &= \Phi \Bigg( &&\sum\limits_{m\in M}r_m\delta _m + r_m'\delta _ m\Bigg)\\
&= &&\sum\limits_{m\in M}(r_m+r_m')\phi (m)\\
&= &&\sum\limits_{m\in M}r_m\phi (m) &+ & &\sum\limits_{m\in M}r_m'\phi (m)\\
&=\Phi \Bigg(&&\sum\limits_{m\in M}r_m\delta _m\Bigg) &+ & \Phi \Bigg(&\sum\limits_{m\in M}r_m'\delta _m\Bigg)
\end{alignat*}
\end{document}
Firstly, the second sigmas in the last two lines don't seem to be aligned.
Second, is there a way to remove that space between those the two plus signs and the terms before them (on the last two lines)?
Thanks!
\documentclass{article} \usepackage{amsmath} \begin{document} \begin{align*} \Phi \Bigl(\sum\limits_{m\in M}r_m\delta _m + \sum\limits_{m\in M}r_m'\delta _m\Bigr) &= \Phi \Bigl( \sum\limits_{m\in M}r_m\delta _m + r_m'\delta _ m\Bigr)\\ &= \sum\limits_{m\in M}(r_m+r_m')\phi (m)\\ &= \sum\limits_{m\in M}r_m\phi (m) + \sum\limits_{m\in M}r_m'\phi (m)\\ &=\Phi \Bigl( \sum\limits_{m\in M}r_m\delta _m\Bigr) + \Phi \Bigl( \sum\limits_{m\in M}r_m'\delta _m\Bigr) \end{align*} \end{document}
I also reduced the parenthesis size.