1

I am trying to make several codes for physics, but I think in the first equation is too small compared another equation. I need your advice for another code.

\begin{gather*} 
\bra{\psi_m}\times\xleftarrow{
i\hbar\sum_{n}\dot{C}(t)_ne^{-iE^{(0)}_nt/\hbar}\ket{\psi_n} =
\sum_{n}H_1C_n(t)e^{-iE^{(0)}_nt/\hbar}\ket{\psi_n}}\\
i\hbar\sum_{n}\dot{C}(t)_ne^{-iE^{(0)}_nt/\hbar}\delta_{m,n} =
\sum_{n}C_n(t)e^{-iE^{(0)}_nt/\hbar}\bra{\psi_m}H_1\ket{\psi_n}\\    
i\hbar\dot{C}(t)_m =
\sum_{n}C_n(t)e^{i(E^{(0)}_m-E^{(0)}_n)t/\hbar}\bra{\psi_m}H_1\ket{\psi_n} \\     
\boxed{\dot{C}(t)_m = -\frac{i}{\hbar}
\sum_{n}C_n(t)e^{i\omega_{mn}t}\bra{\psi_m}H_1\ket{\psi_n}}    
\end{gather*}

enter image description here

4
  • 1
    Add \displaystyle
    – azetina
    Commented Dec 13, 2016 at 7:30
  • It doesn't work with my code.
    – Air.api
    Commented Dec 13, 2016 at 7:34
  • 1
    @Air.api add it here \xleftarrow{\displaystyle ... }. And for me as a reader it feels you should align the = signs Commented Dec 13, 2016 at 7:35
  • In addition to considering \displaystyle in the argument of \xleftarrow, do also consider using \textstyle.
    – Mico
    Commented Dec 13, 2016 at 7:57

2 Answers 2

1

I'm not sure what the meaning should be, but perhaps you want something like this:

\documentclass{article}
\usepackage{amsmath,mathtools,braket}

\begin{document}

\[
\bra{\psi_m}\times
\underleftarrow{
  i\hbar\sum_{n}\dot{C}(t)_ne^{-iE^{(0)}_nt/\hbar}\ket{\psi_n} =
  \sum_{n}H_1C_n(t)e^{-iE^{(0)}_nt/\hbar}\ket{\psi_n}
}
\]

\end{document}

enter image description here

1

I have the following suggestions:

  • For the equation in the first row, consider placing the argument of \xleftarrow in text style; the default is script style, which indeed looks a bit, well, small. Going to display style, on the other hand, seems like too much of a good thing since there's no need to make the summation symbols really big.

  • For the second and third row, consider replacing the e^{...} terms with \exp(...) expressions. Also, consider using the more compact \braket notation instead of having separate \bra and \ket terms.

  • For the fourth row, the only thing you may want to change is using the more compact \braket notation instead of providing \bra and \ket terms.

The following screenshot shows various before-and-after combinations.

enter image description here

\documentclass{article}
\usepackage{mathtools,braket}
\begin{document}

\begin{gather*}
\bra{\psi_m}\times\xleftarrow{% default style for argument is script style
i\hbar\sum_{n}\dot{C}(t)_ne^{-iE^{(0)}_nt/\hbar}\ket{\psi_n} =
\sum_{n}H_1C_n(t)e^{-iE^{(0)}_nt/\hbar}\ket{\psi_n}}\\
\shortintertext{versus}
\bra{\psi_m}\times\xleftarrow{\textstyle
i\hbar\sum_{n}\dot{C}(t)_ne^{-iE^{(0)}_nt/\hbar}\ket{\psi_n} =
\sum_{n}H_1C_n(t)e^{-iE^{(0)}_nt/\hbar}\ket{\psi_n}}\\
\shortintertext{or}
\bra{\psi_m}\times\xleftarrow{\displaystyle
i\hbar\sum\nolimits_{n}\dot{C}(t)_ne^{-iE^{(0)}_nt/\hbar}\ket{\psi_n} 
    \sum\nolimits_{n}H_1C_n(t)e^{-iE^{(0)}_nt/\hbar}\ket{\psi_n}}
\end{gather*}
\hrule
\begin{gather*}
i\hbar\sum_{n}\dot{C}(t)_ne^{-iE^{(0)}_nt/\hbar}\delta_{m,n} =
\sum_{n}C_n(t)e^{-iE^{(0)}_nt/\hbar}\bra{\psi_m}H_1\ket{\psi_n}\\
i\hbar\dot{C}(t)_m =
\sum_{n} C_n(t)e^{i(E^{(0)}_m -E^{(0)}_n)t/\hbar} \bra{\psi_m}H_1\ket{\psi_n}\\
\intertext{versus}
i\hbar\sum_{n}\dot{C}(t)_n\exp(-iE^{(0)}_nt/\hbar)\delta_{m,n} 
= \sum_{n}C_n(t)\exp(-iE^{(0)}_nt/\hbar) \braket{\psi_m|H_1|\psi_n}\\
i\hbar\dot{C}(t)_m 
= \sum_{n} C_n(t)\exp\bigl(i(E^{(0)}_m -E^{(0)}_n)t/\hbar\bigr) \braket{\psi_m|H_1|\psi_n}
\end{gather*}
\hrule
\begin{gather*}
\boxed{\dot{C}(t)_m = -\frac{i}{\hbar} \sum_{n} C_n(t)e^{i\omega_{mn}t}
    \bra{\psi_m}H_1\ket{\psi_n}}\\
\shortintertext{versus}
\boxed{\dot{C}(t)_m = -\frac{i}{\hbar} \sum_{n} C_n(t)e^{i\omega_{mn}t}
    \braket{\psi_m|H_1|\psi_n}}
\end{gather*}

\end{document} 
1
  • thanks @Mico for your suggestion. It's good advice for me.
    – Air.api
    Commented Dec 13, 2016 at 9:21

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