[Tex/LaTex] Align negative decimal numbers in a matrix

Question

How can I align the negative decimal numbers in a matrix which is in a table as siunitx do with numbers in a table (I am using the class elsarticle option:twocolumn)

    \documentclass[5p,twocolumn]{elsarticle}

    \usepackage{booktabs,tabularx}
    \usepackage{amsmath}

\begin{document}
    \begin{table}
    \caption{Algorithm 3 Illustrative calculation for Numerical Example 2}
        \label{tab:Example 2.2}
    %    \centering
    \footnotesize%scriptsize
    \setlength\tabcolsep{1pt}
    \setlength\arraycolsep{2pt}
    \begin{tabular}{ll}
        \toprule
    \normalfont Algorithm steps 
        & Numerical computation\\
        \midrule
    Input  &   Given\\
      & $ \mathbf{U}|_{\theta=0.5} = \begin{bmatrix} -1 & 1 & 0.2298 & 0.5000 & 0.7702 & 0.1250 \end{bmatrix}^T$\\
      & $\mathbf{U}'_{\theta}|_{\theta =0.5} = \begin{bmatrix} -2 & 2 & 0.8415 & 1 & -0.8415 & 0.7500  \end{bmatrix}^T$\\
      & $ \mathbf{v} = \begin{bmatrix} -2.7063 & 1.0000 & 0.2298 & 0.5000 & 0.7702 & 0.1250 \end{bmatrix}^T$\\
      & $ \mathbf{u} = \begin{bmatrix} -0.8905 & 0.3290 & 0.0756 & 0.1645 & 0.2534 & 0.0411 \end{bmatrix}^T$\\
        \midrule
    Step 1: & Compute $\|\mathbf{U}\|'_{\theta} = 2.4257$\\ 
    Step 3: & Compute $\mathbf{v}'_{\theta} =$ \\
       & $\begin {bmatrix} 
        -4.4257 & 2.0000 & 0.8415 & 1.0000 & -0.8415 & 0.7500 
         \end{bmatrix}^T$\\ 
    Step 7: & Compute $\|\mathbf{v}'_{\theta}\| = 4.6451$\\  
    Step 8: & Compute $\mathbf{u}'_{\theta} = $ \\
       & $\begin {bmatrix} 
        -0.0952 & 0.1552 & 0.1613 & 0.0776 & -0.6642 & 0.1839 
         \end{bmatrix}^T$\\
    Step 9: & Compute $ \mathbf{Q}'_{\theta} = $\\
       &   $\begin{bmatrix} 
        -0.3390 &  0.3390 &  0.3017 &  0.1695 & -1.1348 &  0.3354\\ 
         0.3390 &  0.2042 & -0.1296 & -0.1021 &  0.3585 & -0.1338\\ 
         0.3017 & -0.1296 & -0.0488 & -0.0648 &  0.0178 & -0.0411\\
         0.1695 & -0.1021 & -0.0648 & -0.0511 &  0.1792 & -0.0669\\ 
        -1.1348 &  0.3585 &  0.0187 &  0.1792 &  0.6733 & -0.0386\\ 
         0.3354 & -0.1338 & -0.0411 & -0.0669 & -0.0386 & -0.0303
            \end{bmatrix}$\\
    Step 10: & Extract $\mathbf{Q}'_{\theta} = \mathbf{Q}'_{\theta}(1,1:6)= $\\ 
      &$\begin{bmatrix} -0.3390 & 0.3390 & 0.3017 & 0.1695 & -1.1348 & 0.3354 \end{bmatrix}^T$\\
    Step 11: & $\mathbf{R}'_{\theta} = \begin{bmatrix} 2.4257 \end{bmatrix}$ \\
    \midrule
    Output & $\mathbf{R}'|_{\theta = 0.5} = \begin{bmatrix} 2.4257 \end{bmatrix}$\\
    \midrule
    Test & Accuracy of the computations:\\
    & $\|(\mathbf{U}^T\mathbf{U})'_{\theta}|_{\theta=0.5} - (\mathbf{R}^T\mathbf{R})'_{\theta}|_{\theta=0.5}\|=1.7764\cdot10^{-15}$\\
    \bottomrule
    \end{tabular}
    \end{table}
\end{document}

Answer 1

Since all your numbers have the exact same number of digits but only differ by having a minus sign or not, the easiest thing to do is to right-align the columns of the matrix, using the bmatrix* environment from the mathtools package. See the answers to this question for more ways of aligning matrix elements.

\documentclass[5p,twocolumn]{elsarticle}

\usepackage{booktabs,tabularx}
\usepackage{amsmath}
\usepackage{mathtools}

\begin{document}

\footnotesize
\setlength\tabcolsep{1pt}
\setlength\arraycolsep{2pt}
\begin{tabular}{ll}
    Step 9: & Compute $ \mathbf{Q}'_{\theta} = $\\
    & $\begin{bmatrix*}[r] 
    -0.3390 &  0.3390 &  0.3017 &  0.1695 & -1.1348 &  0.3354\\ 
     0.3390 &  0.2042 & -0.1296 & -0.1021 &  0.3585 & -0.1338\\ 
     0.3017 & -0.1296 & -0.0488 & -0.0648 &  0.0178 & -0.0411\\
     0.1695 & -0.1021 & -0.0648 & -0.0511 &  0.1792 & -0.0669\\ 
    -1.1348 &  0.3585 &  0.0187 &  0.1792 &  0.6733 & -0.0386\\ 
     0.3354 & -0.1338 & -0.0411 & -0.0669 & -0.0386 & -0.0303
    \end{bmatrix*}$
\end{tabular}

\end{document}