# Vector diagram using Tikz

How would one go about producing the following vector diagram using TikZ?

• How far did you go? Where is the point that really bothers you? Commented Aug 18, 2015 at 2:17
• Are the ellipses supposed to have the same radii? Commented Aug 18, 2015 at 2:29

Here's one possibility; since no information was given in the question, I assumed that "I" and "J" were arbitrarily placed:

The code:

\documentclass[border=3pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}[>=latex]
\coordinate (O) at (0,0);
\coordinate (I) at ([shift={(30:2cm)}]O);
\coordinate (J) at ([shift={(120:5cm)}]O);
\coordinate (F) at ( $(I)+(J)$ );
% the circles (ellipses)
\draw
let
\p1=(I),
\p2=(J)
in
% the vector lines
\foreach \Valor in {I,J,F}
\draw[->] (O) -- (\Valor);
% the dashed lines
\draw[dashed]
(J) -- (F) -- (I);
% the labels
\foreach \Valor/\Pos in {O/below,I/right,J/left,F/above}
\node[\Pos] at (\Valor) {$\Valor$};
% axis lines (optional)
\draw[gray!20]
(O) -- ++(0pt,6cm);
\draw[gray!20]
([xshift=-3cm]O) -- ([xshift=3cm]O);
\end{tikzpicture}

\end{document}

If the circles (ellipses) should be of the same radii, the code is even shorter:

\documentclass[border=3pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}[>=latex]
\def\PosCirci{1}
\def\PosCircii{5}
\coordinate (O) at (0,0);
\draw
\coordinate (F) at ( $(I)+(J)$ );
% the vactor lines
\foreach \Valor in {I,J,F}
\draw[->] (O) -- (\Valor);
% the dashed lines
\draw[dashed]
(J) -- (F) -- (I);
% the labels
\foreach \Valor/\Pos in {O/below,I/right,J/left,F/above}
\node[\Pos] at (\Valor) {$\Valor$};
\end{tikzpicture}

\end{document}

• thanks for that! I left the question without any explanation of the symbols. I and J are angular momentum vectors, whose vector sum is F. And yes, they are indeed arbitrarily placed. Commented Aug 18, 2015 at 5:00