problem when writing an equation with latex: missing delimiter (. inserted) \end{equation}

Question

I tried this and that, but could not solve this problem. Here is the code that produces this error:

\begin{equation}
o=g(h)=\left\{\begin{array}{rcl}
    1 & if & h <   0 \\
    0 & if & h \le 0 
\end{array}\right
\end{equation}

The error is given on the line \end{equation} resides. Thanks.

Answer 1

\left\{ must be balanced by a \right\} in the same line. Since you don't want the right delimiter, and since the closing pair is needed, you have to put a null delimiter by \right.

\documentclass{article}
\begin{document}
  \begin{equation}
    o=g(h)=\left\{\begin{array}{rcl}
                     1 & if & h <   0 \\
                     0 & if & h \le 0
\end{array}\right.  %% <--here
\end{equation}
\end{document}

But for this amsmath provides cases environment. I suggest you to use this. A sample will be:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
  \begin{equation}
    o=g(h)=\begin{cases}
              1 & \text{if $ h < 0 $}\\
              0 & \text{if $ h \le 0$}
\end{cases}
\end{equation}
\end{document}

Note the use of \text macro which is also provided by amsmath.

Answer 2

\begin{numcases}{|x|=} 
x, & for $x \geq 0$ \label{eq:4}
\\ -x, & for$x < 0$ \label{eq:5} 
\end{numcases}

You have to use

\usepackage{cases}