Difficulty with \flalign

Consider the following example.

\begin{flalign}
&Max Z=a+b\\
&Min P=c-d\\
&\mbox{subject to}\\
&a \leq 10\\
&c \geq 5
\end{flalign}


When I run it I get the desired output, but the only problem is I do not want "subject to" to get numbered. So if I modify it, and write something like

\begin{flalign}
&Max Z=a+b\\
&Min P=c-d
\end{flalign}
subject to
\begin{flalign}
&a \leq 10\\
&c \geq 5
\end{flalign}


then my alignment between the first set of equations and the second set of equations gets disturbed.

How do I proceed?

-
First of all you shouldn't use flalign, but align; use \notag in the “subject to” line. –  egreg Jun 20 at 18:03

As @egreg said, use align. Also, with mathtools you can use \shortintertext

\documentclass{report}
\usepackage{mathtools}

\begin{document}\pagestyle{empty}

\begin{align}
\max  Z &=a+b\\
\min  P &=c-d\\
\shortintertext{subject to}
a &\leq 10\\
c &\geq 5
\end{align}


Also, use \min and \max.

-

I suggest one of these this variant, using llap:

\documentclass{report}

\usepackage{mathtools}

\begin{document}\pagestyle{empty}
Text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text.
\begin{align}
\max Z &=a+b \\
\min P &=c-d \\[1ex]
\text{\llap{subject to: \hskip 2em}} a &\leq 10 \\
c &\geq 5
\end{align}

\begin{flalign}
& & \max Z &=a+b & & \\
& & \min P &=c-d \\[1ex]
& \text{\rlap{subject to: }} & a &\leq 10 \\
& & c &\geq 5
\end{flalign}
More text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text.

\end{document}


-
I would like this variant, but with the subject correctly aligned to the left. I hope the “next version” of a basic math package includes something like \shortintertext but in the same line instead of creating a new one. –  Manuel Jun 20 at 18:48
Look at my edit: with flalign one can do what you want, I think. –  Bernard Jun 20 at 19:00
I know, but it's less “robust”, I mean, you have to think, to add &, it's less automatic. –  Manuel Jun 20 at 19:06
That's true; however you have to put 5 & only in the first line, then only 3. I agree it would be a syntax simpler if we had a sort of \intext or \leftag command. Note that if your equation numbers were on the left, the \tag command would do the trick. –  Bernard Jun 20 at 19:16