I'm new to latex and all of my matrices seem to be created on new lines, I can't seem to put them side by side. Here is what I am doing to make a matrix (with the 2d identity matrix as an example):

\[ \left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right) \]

Am I making it wrong? How can I place a second matrix directly beside this, as you would when doing matrix mathematics? Thanks

up vote 22 down vote accepted

Don't enclose each array with \[ ... \]; instead, put all the arrays that you want together within one set of delimeters. Like this:

\[ \left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right)
%
\left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right)
\]

You should read the mathmode documentation. It should be part of your TeX Distribution, and has lots of examples to follow.

  • This makes sense. However, does this still handle things like [Matrix][vector] = [vector] all one one line? – user3231 Jan 29 '11 at 20:49
  • @bbel Sure. As long as they will fit on the same line, you can just put them one after another like this (no blank lines in between which is why I separated the two matrices in my example with a % (comment character)). – Alan Munn Jan 29 '11 at 20:52

This is slightly tangential, but you might find it convenient to use the pmatrix environment (defined in amsmath.sty)

\[
\begin{pmatrix}
  1 & 0 \\ 0 & e^{i\pi/k}
\end{pmatrix}
\begin{pmatrix}
  u \\ v
\end{pmatrix}
=
\begin{pmatrix}
  u \\ -v
\end{pmatrix}
\]

The idea is to enclose both matrices in one block i.e. \[ \] see this example

\[
\begin{bmatrix}
    a  &  b      \\
    c  &  d      
\end{bmatrix}
= 
\begin{bmatrix}
    8  &  1      \\
    7  &  6      
\end{bmatrix} 
\]

It will be something like:

enter image description here

  • This is already covered by the other answer(s). – Werner Oct 19 '16 at 4:27

like this

\[ \left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right) \times \left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right) =\left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right)\] 

You need to place the matrices inside the math environment

  • Inside the math environment by surrounding them with the dollar sign operator? Because that gives me errors in itself.. – user3231 Jan 29 '11 at 20:45
  • 1
    \[..\] is a math environment When you use this environment the math expression is written on a single line. Like Alan, I think you should read the mathmode.pdf documentation from Herbert Voss. – Alain Matthes Jan 29 '11 at 21:18

I was confused by the answers and the syntax so I'll share mine and include an image. I'm using \begin{equation} which is arguably less convenient but also more verbose for beginners (like myself) than using the \[ syntax.
To be clear, what is causing the matrices to be on separate lines is the blank line between the min the code. If you fill it with the placeholder % or remove the line completely it will render like the attached picture. (Thanks to Teepeemm for clarifying what % is!)

\begin{equation}
  \begin{bmatrix}
    C_1 & C_2 & C_3 & C_4 
  \end{bmatrix}
  %
  \begin{bmatrix}
    z_1 \\
    z_2 \\
    z_3 \\
    z_4 \\
  \end{bmatrix} 
\end{equation}

two matrices/arrays on the same line

  • The % in the middle is a place holder that doesn't need to be there. TeX doesn't allow have a blank line, so the % gives a line that isn't blank but doesn't have any consequences. Also, the \[ syntax is equivalent to \begin{equation*}. \begin{equation} (without the *) will number the equation. – Teepeemm Dec 5 at 15:29
  • Thanks for your clarification on the %. That explains why my matrices didn't line up side-by-side when adding a space between them. They do however line up correctly without the % and without an empty line between them. Thanks for clearing that up for me! :) I'll modify my answer. – Emanuel Lindström Dec 6 at 17:30

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