Math & Science ⇒ subequation numbering

[kal]

hi,

I have to write my thesis and there are a lot of equations which are grouped into blocks.
some of them are getting their own numbers, some of them are pairs, so they are "subequationed", but i want these blocks to look like a block -> so the amsmath align would be nice. my problem is, that i can't set the subeqations into an align and so different subequations in one block would get different aligns.

one of these blocks should look like:


equ equ (1a,b)
equation (2)
equation (3a)
equation (3b)
equation (4)
equation (5a)
equation (5b)

i already changed the first line to something like

equ (1a) equ (1b)

but would prefer the first variant, because that equations are definitions of variables to which I won't refer.
align would be nice for &= as the left sides of the equations aren't of equal length.

hope i could describe my problem in a proper way

thx

[kal]

till now i wasn't able to solve my problem. But maybe a piece of code is helpful for understanding my problem

Code: Select all

\documentclass[fleqn]{article}
\usepackage{amsmath}

\begin{document}

\begin{subequations}\label{eq:1}
\begin{minipage}{0.45\textwidth}
\begin{align}
\label{eq:1a}
X&=\frac{X}{X+X}
\end{align}
\end{minipage}
\begin{minipage}{0.45\textwidth}
\begin{align}
\label{eq:1b}
X&=\frac{X}{X+X}
\end{align}
\end{minipage}
\end{subequations}
\begin{subequations}\label{eq:2}
\begin{align}
\label{eq:2a}
\frac{\partial X}{\partial X}&=X\cdot\Delta X-\left( X+X \right)X\\
\label{eq:2b}
\frac{\partial X}{\partial X}&=XX-\left( X+X \right)X
\end{align}
\end{subequations}
blablablabla blablablabla
blabla

\begin{subequations}\label{eq:3}
\begin{minipage}{0.45\textwidth}
\begin{align}
\label{eq:3a}
X&=X-X
\end{align}
\end{minipage}
\begin{minipage}{0.45\textwidth}
\begin{align}
\label{eq:3b}
X&=X-X
\end{align}
\end{minipage}
\end{subequations}
\begin{align}
\label{eq:4}
X X&=XX
\end{align}
\begin{subequations}\label{eq:5}
\begin{align}
\label{eq:5a}
\frac{\partial X}{\partial X}&=X\cdot\Delta X-\left( X+X\right)X\\
\label{eq:5b}
\frac{\partial X}{\partial X}&=XX-\left( X+X \right)X
\end{align}
\end{subequations}

\end{document} 

As u can see the structur of the equation-blocks is a bit disarranged.
Hope someone has an idea for me, till now I'm kind of lost, as a latex newbie