اگر $f\left( x \right)=\left\{ \begin{matrix}
ax-1\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\lt 1 \\
{{x}^{2}}+2a\,\,\,\,\,\,\,\,\,\,\,\,\,x\ge 1 \\
\end{matrix} \right.$ و $\underset{x\to {{1}^{+}}}{\mathop{\lim }}\,f\left( x \right)-\underset{x\to {{1}^{-}}}{\mathop{\lim }}\,f\left( x \right)=-1$، مقدار $a$ کدام است؟