Coloring the Vertices of a Grid

Oct 13, 2025 by wbrum.org 107 views

Introduction

When working with TikZ, a powerful drawing package in LaTeX, you often need to perform calculations and manipulate data within your nodes. One such feature is pgfmathresult, which allows you to store the result of a mathematical expression and use it within your node. In this article, we will explore how to use pgfmathresult within a node, with a specific focus on coloring the vertices of a grid.

What is pgfmathresult?

pgfmathresult is a special variable in TikZ that stores the result of a mathematical expression. You can use it within your node to perform calculations and manipulate data. For example, you can use it to calculate the position of a node, the size of a shape, or even the color of a fill.

Coloring the Vertices of a Grid

Let's say you want to color the vertices of a grid one of three colors. You can use pgfmathresult to achieve this. Here's an example code snippet:

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
  \foreach \i in {0,1,2} {
    \foreach \j in {0,1,2} {
      \pgfmathparse{int(mod(\i+\j,3))}
      \node[circle, fill=\pgfmathresult, draw=black] at (\i,\j) {};
    }
  }
\end{tikzpicture}

\end{document}

In this code snippet, we use a nested foreach loop to create a 3x3 grid. We use pgfmathparse to calculate the result of the expression int(mod(\i+\j,3)), which gives us a value between 0 and 2. We then use this value to set the fill color of the node using \pgfmathresult.

How it Works

Here's a step-by-step explanation of how the code works:

The outer foreach loop iterates over the values 0, 1, and 2.
The inner foreach loop iterates over the values 0, 1, and 2.
For each pair of values (\i, \j), we calculate the result of the expression int(mod(\i+\j,3)) using pgfmathparse.
We store the result in the variable \pgfmathresult.
We use the value of \pgfmathresult to set the fill color of the node using \pgfmathresult.

Tips and Variations

Here are some tips and variations to help you get the most out of pgfmathresult:

Use different mathematical expressions: You can use different mathematical expressions to calculate the result. For example, you can use int(mod(\i+\j,4)) to get a value between 0 and 3.
Use different data types: You can use different data types to store the result. For example, you can use real instead of int to get a decimal value.
Use conditional statements: You can use conditional statements to set the fill color based on the result. For example, you can use ifthenelse to set the fill color to red if the result is 0, blue if the result is 1, and green if the result is 2.

Conclusion

In this article, we explored how to use pgfmathresult within a node to color the vertices of a grid. We saw how to use a nested foreach loop to create a 3x3 grid and how to use pgfmathparse to calculate the result of a mathematical expression. We also saw some tips and variations to help you get the most out of pgfmathresult. With this knowledge, you can create complex and beautiful diagrams using TikZ.

Common Issues and Solutions

Here are some common issues and solutions to help you troubleshoot your code:

Error: Unknown function pgfmathparse: Make sure you have included the pgfmath package in your document.
Error: Unknown variable \pgfmathresult: Make sure you have used the pgfmathparse function to calculate the result.
Error: Unknown data type int: Make sure you have used the correct data type to store the result.

Additional Resources

Here are some additional resources to help you learn more about TikZ and pgfmathresult:

TikZ Manual: The official TikZ manual is a comprehensive resource that covers all aspects of TikZ.
TikZ Examples: The TikZ examples page on the CTAN website provides a wealth of examples and code snippets to help you learn TikZ.
Stack Exchange: The Stack Exchange community is a great resource for asking questions and getting help with TikZ and pgfmathresult.
Using pgfmathresult within a node: A Q&A Guide ===========================================================

Introduction

In our previous article, we explored how to use pgfmathresult within a node to color the vertices of a grid. However, we know that there are many more questions and scenarios that you may encounter when working with pgfmathresult. In this article, we will answer some of the most frequently asked questions and provide additional guidance on how to use pgfmathresult effectively.

Q: What is the difference between `pgfmathparse` and `pgfmathresult`?

A: pgfmathparse is a function that calculates the result of a mathematical expression and stores it in a variable. pgfmathresult is a special variable that stores the result of the last pgfmathparse function. In other words, pgfmathparse is used to calculate the result, while pgfmathresult is used to access the result.

Q: How do I use `pgfmathresult` within a node?

A: To use pgfmathresult within a node, you need to use the \pgfmathresult variable within the node options. For example:

\node[circle, fill=\pgfmathresult, draw=black] at (0,0) {};

This code sets the fill color of the node to the result of the last pgfmathparse function.

Q: Can I use `pgfmathresult` with other TikZ commands?

A: Yes, you can use pgfmathresult with other TikZ commands. For example, you can use it to set the position of a node:

\node[circle, fill=\pgfmathresult, draw=black] at (\pgfmathresult,0) {};

This code sets the position of the node to the result of the last pgfmathparse function.

Q: How do I handle errors when using `pgfmathresult`?

A: When using pgfmathresult, you may encounter errors if the result is not a valid value. To handle errors, you can use the ifthenelse function to check if the result is valid before using it. For example:

\pgfmathparse{int(mod(\i+\j,3))}
\ifthenelse{\pgfmathresult>0}{\node[circle, fill=\pgfmathresult, draw=black] at (\i,\j) {}}{}

This code checks if the result is greater than 0 before using it to set the fill color of the node.

Q: Can I use `pgfmathresult` with other LaTeX commands?

A: Yes, you can use pgfmathresult with other LaTeX commands. For example, you can use it to set the value of a LaTeX variable:

\newcommand{\myvar}{\pgfmathresult}

This code sets the value of the LaTeX variable \myvar to the result of the last pgfmathparse function.

Q: How do I reset the value of `pgfmathresult`?

A: To reset the value of pgfmathresult, you can use the \pgfmathreset function. For example:

\pgfmathreset

This code resets the value of pgfmathresult to an empty string.

Q: Can I use `pgfmathresult` with other packages?

A: Yes, you can use pgfmathresult with other packages. For example, you can use it with the pgfplots package to create plots with dynamic data. For example:

\documentclass{article}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
\pgfmathparse{int(mod(\i+\j,3))}
\addplot[only marks, mark size=2pt, mark options={fill=\pgfmathresult}] coordinates {(\i,\j)};
\end{tikzpicture}
\end{document}

This code creates a plot with dynamic data using the pgfplots package and the pgfmathresult variable.

Conclusion

In this article, we answered some of the most frequently asked questions and provided additional guidance on how to use pgfmathresult effectively. We hope that this article has been helpful in your journey to master the art of using pgfmathresult within a node.