# why the symbols does not render correctly?

I have a equation array command including 3 line of equation. In the first and second lines the all is correct but in the third line none of the symbols render correctly. I checked this issue with various online LaTeX editor and persisted on all of them.

Can anyone tell me what is wrong?

\begin{eqnarray}
ds^{2}=\frac{\tilde{L}^2}{z^{2}}\left(\left(1-
f(v,z)v'^{2}-2z'v'\right)dx^{2}+dx_2^{2}+dx_3^{2}\right)\\
\sqrt{h}=\frac{\tilde{L}^3}{z^{3}}\left(1-
\sqrt{\sigma}=\frac{\tilde{L}^{2}}{z^{2}}\\
\sqrt{h} \cal{R}_{\Sigma}=-\frac{2\tilde{L} Q'z'}{Q^{\frac{3}{2}}z^{2}}-
\frac{6\tilde{L} z'^{2}}{\sqrt{Q}z^{3}}+\frac{4\tilde{L} z''}
{\sqrt{Q}z^{2}}\\
\sqrt{h}\cal{R}_{\Sigma}=-\frac{2 \tilde{L} Q'z'}{Q^{\frac 32}z^{2}}-
\frac{6\tilde{L}z'^{2}}{\sqrt{Q}z^{3}}+\frac{4\tilde{L}z''}{\sqrt{Q}z^{2}}
\end{eqnarray}

• \cal is not intended for use in math. try to replace it with \mathcal. – Zarko Sep 23 '17 at 4:18

• the \cal command was used in LaTeX 2.09 and has been obsolete since the release of LaTeX2e (1992). It worked as a font change declaration rather than a command with argument, therefore its correct use is {\cal ...}. instead it use \mathcal
• off-topics: instead eqnarray rather use align or gather (as you use eqnarray)

\documentclass{article}
\usepackage{amsmath}

\begin{document}
with "garther":
\begin{gather}% changed
ds^{2}=\frac{\tilde{L}^2}{z^{2}}\left(\left(1-
f(v,z)v'^{2}-2z'v'\right)dx^{2}+dx_2^{2}+dx_3^{2}\right)\\
\sqrt{h}=\frac{\tilde{L}^3}{z^{3}}\left(1-
\sqrt{\sigma}=\frac{\tilde{L}^{2}}{z^{2}}\\
%
\sqrt{h} \mathcal{R}_{\Sigma}
=-\frac{2 \tilde{L} Q'z'}
{Q^{\frac{1}{2}} z^{2}} -
\frac{6\tilde{L} z'^{2}}{\sqrt{Q}z^{3}}+\frac{4\tilde{L} z''}
{\sqrt{Q}z^{2}}\\
%
\sqrt{h}\mathcal{R}_{\Sigma}=-\frac{2}{\tilde{L} Q'z'}{Q^{\frac 32}z^{2}}-
\frac{6\tilde{L}z'^{2}}{\sqrt{Q}z^{3}}+\frac{4\tilde{L}z''}{\sqrt{Q}z^{2}}
\end{gather}

with "align":
\begin{align}% changed
ds^{2}
& = \frac{\tilde{L}^2}{z^{2}}
\left(\left(1 - f(v,z)v'^{2} - 2z'v'\right) dx^{2} + dx_2^{2}+dx_3^{2}\right)        \\
\sqrt{h}
& = \frac{\tilde{L}^3}{z^{3}}
\left(1 - f(v,z)v'^{2}-2z'v'\right)^{\frac{1}{2}},
\sqrt{\sigma}=\frac{\tilde{L}^{2}}{z^{2}}\\
%
\sqrt{h} \mathcal{R}_{\Sigma}% <-- changed
& = -\frac{2 \tilde{L} Q'z'}{Q^{\frac{1}{2}} z^{2}} -
\frac{6\tilde{L} z'^{2}}{\sqrt{Q}z^{3}} +
\frac{4\tilde{L} z''}{\sqrt{Q}z^{2}}\\
%
\sqrt{h}\mathcal{R}_{\Sigma}% <-- changed
& = -\frac{2}{\tilde{L} Q'z'}{Q^{\frac 32}z^{2}} -
\frac{6\tilde{L}z'^{2}}{\sqrt{Q}z^{3}} +
\frac{4\tilde{L}z''}{\sqrt{Q}z^{2}}
\end{align}
\end{document} • Very thanks. it is very interesting why in some line the \cal works but in another line does not. Anyway I used, as you mentioned, \mathcal and solved my problem. – PhysicsExams Sep 23 '17 at 5:40
• The \cal command was used in LaTeX 2.09 and has been obsolete since the release of LaTeX2e (1992). It worked as a font change declaration rather than a command with argument. see tex.stackexchange.com/questions/84041/why-does-calm-n-give-m – Zarko Sep 23 '17 at 6:08