Is it possible to flush left equations using “numcases” or “subnumcases”?

Question

I am wondering if it is possible in LaTeX to flush left equations when using the numcases or subnumcases environment provided by the cases package.

Hereafter I include a bit of code to explain the problem.

\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[fleqn]{mathtools}
\usepackage{cases}

\begin{document}
\begin{equation}
\tau = k \cdot i_a
\end{equation}
\begin{numcases}{v_a = }
v_s - k_1 \cdot (i_a - i) & if ia\\
v_p     &   if ia $\le$ i
\end{numcases}
\begin{subnumcases}{v_a = }
v_s - k_1 \cdot (i_a - i) & if ia\\
v_p     &   if ia $\le$ i
\end{subnumcases}
\end{document}

Compiling this code, you will see that the first equation is flushed left while the other two are not. I would appreciate any suggestions.

Answer 1

The cases package has a fleqn option:

 \usepackage[fleqn]{cases}