How to have multiple arrows pointing from individual parts of one equation to another?

Question

I want to get a similar and simple effect like this that doesn't involve crazy arrow curves or packages.

Answer 1

I'm adapting my answer to "How to add arrow in equations and matrix?" to your example; check it out for some explanations. Basically, you have to

• wrap all parts that you want to reference in the drawing commands into a \tikznode command, which assigns a name to it and stores the size of the box

• add a tikzpicture environment starting with

  \begin{tikzpicture}[remember picture,overlay,...]
  

  that contains the draw commands.

• run LaTeX twice to get the positions right.

\documentclass{article}
\usepackage{amsmath,amssymb}
\usepackage{tikz}
\newcommand\tikznode[3][]%
   {\tikz[remember picture,baseline=(#2.base)]
      \node[minimum size=0pt,inner sep=0pt,#1](#2){#3};%
   }
\begin{document}
\begin{align*}
  \tikznode{PT}{$P_{T}$} &=
  \tikznode{PB0}{$P^{0}_{B}$}+X_{A}(\tikznode{diff}{$\underbrace{P^{0}_{A}-P^{0}_{B}}$}) \\[2ex]
  \tikznode{y}{$y$} & =  \tikznode{a}{$a$}+ \tikznode{b}{$b$}\cdot x
\end{align*}
\begin{tikzpicture}[remember picture,overlay,cyan,rounded corners,>=stealth,shorten > =1pt,shorten <=1pt,thick]
  \draw[->] (PT) -- (y);
  \draw[->] (PB0) -- (a);
  \draw[->] (diff) -- +(0,-0.5) -| (b);
\end{tikzpicture}
\end{document}

Answer 2

This is one of many solution to create your image...I have not used TikZ but a simple environment array. Just to be correct considering that the moving of the characters was done manually with \mkern, whenever you added something the arrows would move and not be aligned as in the example.

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\begin{document}
\[
\begin{array}{ll}
P_{T} &= P^{0}_{B}+X_{A}(\underbrace{P^{0}_{A}-P^{0}_{B}}) \\[-.4ex]
\downarrow & \quad \downarrow \mkern85mu \swarrow\\
y & =  a+\mkern50mu b\cdot x
\end{array}   
\]
\end{document}

Answer 3

Here is a possibility with pstricks:

\documentclass[svgnames]{article}
\usepackage{mathtools}
\usepackage{amssymb, bm} 
\newcommand{\mathbsf}[1]{\bm{\mathsf{#1}}}
\usepackage{pst-node}
\begin{document}
\begin{alignat}{2}
 \rnode{PT}{P_T} & ={} & \rnode{PB}{P_B⁰} & + X_A\bigl(\underbrace{P_A-P_B^0}_{\pnode[-3pt, 1.5ex]{PAB}}\bigr) \[1.5ex]
\rnode{y}{\mathbsf{y}} & ={} & \rnode{a}{\mathbsf{a}} & \mathbin{\mathbsf{+}} \rnode{b}{\mathbsf{b}}\cdot \mathbsf{x}
\psset{arrows=->, arrowinset=0.12, linecolor=DeepSkyBlue, nodesep=1pt}
\ncline{PT}{y}
\ncline{PB}{a}
\ncline{PAB}{b}
 \end{alignat}
\end{document} } 

Answer 4

You should be to use the tikz to make arrows in the equation like example below.

\documentclass[10pt,a4paper]{article}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{arrows}
\begin{document}
    \begin{equation}
        \begin{tikzpicture}
        \node (E1) at (0,0.71) {$P_{T} = P^{0}{B}+X{A}(\underbrace{P^{0}{A}-P^{0}{B}})$};
        \node (E2) at (0,0) {$Y = A + B X$};
        \draw[->,thick] (-0.7,.6)--(-0.1,0.2); 
        \draw[->,thick] (1.2,.5)--(0.6,0.2); 
        \draw[->,thick] (-1.7,.7)--(-1.1,0.2); 
        \end{tikzpicture}
    \end{equation}
\end{document}

Good luck