# How can I properly format this?

Can I use another proper format instead of this? This is my code

(s_{d+i})_k=\sum_{j=0}^{d-1}\lambda_j(s_{j+i})_k \qquad  & 0\leqslant i\leqslant d-1\\  & 1\leqslant k\leqslant d

• I have slightly changed the second solution, you might want to look at it. – egreg Jun 20 '18 at 20:40
• @egreg what actually change? ps with the new mod I get some errors – malloc Jun 20 '18 at 20:50
• I exploited array features better; but you need \usepackage{array} in addition to your other loaded packages. – egreg Jun 20 '18 at 20:53

The fact that you need to stack the conditions seems to point to a two column format, otherwise just continuing on the same line would be sufficient.

\documentclass[twocolumn]{article}
\usepackage{amsmath,amssymb}

\usepackage{lipsum} % for context

\begin{document}

\lipsum*[3]
(s_{d+i})_k=\sum_{j=0}^{d-1}\lambda_j(s_{j+i})_k \qquad \begin{aligned} & 0\leqslant i\leqslant d-1\\ & 1\leqslant k\leqslant d \end{aligned}
\lipsum

\end{document}


You can get less vertical space between the conditions with array, also with alignment of the inequality symbols:

\documentclass[twocolumn]{article}
\usepackage{amsmath,amssymb,array}

\usepackage{lipsum} % for context

\begin{document}

\lipsum*[3]
$(s_{d+i})_k=\sum_{j=0}^{d-1}\lambda_j(s_{j+i})_k \qquad \setlength{\arraycolsep}{0pt} \begin{array}{c>{{}}c<{{}}c>{{}}c<{{}}l} 0 &\leqslant& i &\leqslant& d-1\\ 1 &\leqslant& k &\leqslant& d \end{array}$
\lipsum

\end{document}


Here is another possibility:

\documentclass{article}
\usepackage{amssymb}
\usepackage{mathtools}
\usepackage[showframe]{geometry}

\begin{document}

\begin{gather}
(s_{d+i})_k =\sum_{j=0}^{d-1}\lambda_j(s_{j+i})_k \tag*{\llap{$(0\leqslant i\leqslant d-1 ,\enspace 1\leqslant k\leqslant d)$}}
\end{gather}

\end{document}