I used the following code to make sections in nomenclature. This totally works. While I wanted to add the fourth section "Matrices" which is now commented out I faced with an error. I attached the photo of the error. Any help appreciated.
\renewcommand{\nomgroup}[1]{%
\ifthenelse{\equal{#1}{A}}{\item[{Sets and Indicis:}]}{%
\ifthenelse{\equal{#1}{B}}{\item[{Variables:}]}{%
%\ifthenelse{\equal{#1}{B}}{\item[{Parameters:}]}{%
\ifthenelse{\equal{#1}{D}}{\item[{Cons}]}{}}}
}
\makenomenclature
\nomenclature[A1]{$\Omega_N$}{Set of all buses (nodes).}
\nomenclature[A2]{$n,m$}{Index of all buses (nodes). $m$ is alias of $n$.}
\nomenclature[A3]{$\Omega_L$}{Set of all Transmission lines.}
\nomenclature[A4]{$l$}{Index of transmission lines.}
\nomenclature[A5]{$\Omega_{K}$}{Set of all genetors.}
\nomenclature[A6]{$k$}{Index of generator $k\in\Omega_{k}.$}
\nomenclature[A7]{$\Omega_{D}$}{Set of all demand buses.}
\nomenclature[A8]{$d$}{Index of demand, $d\in\Omega_{D}.$\\}
\nomenclature[B1]{$\theta_{n}$}{Voltage angle at bus $n.$}
\nomenclature[B2]{$v_n$}{Voltage magnitude at bus $n.$}
\nomenclature[B3]{$p_{nk}$}{Real power supply from generator $k$ at bus $n.$}
\nomenclature[B4]{$q_{nk}$}{Reactive power supply from generator $k$ at bus$n.$}
\nomenclature[B5]{$p_{nml}$}{Active power flows from bus $m$ to bus $n$ through transmission line $l.$}
\nomenclature[B6]{$\lambda_{nml}$}{compansation level of transmission line $l$ between bus $n$ and $m$.}
\nomenclature[B7]{$u_{nml}$}{Binary variable denoting the placement of TCSC on line $l$ between bus $m$ and $n.$\\}
\nomenclature[D1]{$c_k$}{Cost coefficient of generator $k.$}
\nomenclature[D2]{$p_{nd}$}{Real power demand at bus $n.$}
\nomenclature[D3]{$q_{nd}$}{Reactivel power demand at bus $n.$}
\nomenclature[D4]{$r_{nml}$}{Resistance of transmission line $l$ between bus $m$ and $n.$}
\nomenclature[D5]{$x_{nml}$}{Reactance of transmission line $l$ between bus $m$ and $n$ .}
\nomenclature[D6]{$g_{nml}$}{Conductance of transmission line $l$ between bus $m$ and $n$ .}
\nomenclature[D7]{$b_{nml}$}{Susceptance of transmission line $l$ between bus $m$ and $n$ .}
\nomenclature[D8]{$x_{nml}^{'}$}{Reactance of transmission line $l$ after compansation.}
\nomenclature[D9]{$g_{nml}^{'}$}{Conductance of transmission line $l$ after compansation.}
\nomenclature[D10]{$b_{nml}^{'}$}{Sueceptance of transmission line $l$ after compansation.}
\nomenclature[D11]{$p_{k}^{min}$ ,$p_{k}^{max}$}{Lower and upper bound of active power supplied by generator$ k.$}
\nomenclature[D12]{$p_{k}^{min}$ ,$p_{k}^{max}$}{Lower and upper bound of reactive power supplied by generator$ k.$}
\nomenclature[D13]{$\theta_{n}^{min}$, $\theta_{n}^{max}$}{Lower and upper bound of voltage angle at bus $n.$}
\nomenclature[D14]{$v_{n}^{min}$, $v_{n}^{max}$}{Lower and upper bound of voltage magnitude at bus $n.$}
\nomenclature[D15]{$\lambda^{max}$}{Maximum available compansation level.}
\nomenclature[D16]{$\eta_{TCSC}$}{Number of available TCSCs.}
\nomenclature[D17]{$M$}{Big integer number.}
\nomenclature[D18]{$N_{b}$}{ Number of buses ($\mid\Omega_{N}\mid=N_{b}$).}
\nomenclature[D19]{$N_{l}$}{Number of transmission lines ($\mid\Omega_{L}\mid=N_{l}$).}
\nomenclature[D20]{$\mu_l$}{Dual variable regarding to change in active power generation of unit $k$ in subproblem.}
\nomenclature[D21]{$\alpha_k$}{Dual variable regarding to change in active power generation of unit $k$ in subproblem.}
\nomenclature[D22]{$\beta_l$}{Dual variable in adjusting compansation level of TCSC in trasmission line $l$.}
\nomenclature[D23]{$N_{k}$}{ Number of generators ($\mid\Omega_{K}\mid=N_{k}$).}
%\nomenclature[G1]{}{}
\printnomenclature
Best Answer
You are simply missing a closing brace.
should be
MWE:
Output: