I have to use the \documentclass[<options>]{cas-dc} , and also I have used the following packages in my document in Latex.
The default style of the summation symbol in the document class cas-dc is:
How can I change it to the following style?
\documentclass[a4paper,fleqn]{cas-dc}
\usepackage{lipsum,capt-of,graphicx}
\usepackage{geometry}
\usepackage{natbib}
\usepackage{ragged2e}
\usepackage{setspace}
\usepackage[labelfont=bf,justification=raggedright,singlelinecheck=false, font={footnotesize}]{caption}
\captionsetup[figure]{name=Fig. ,labelsep=period, justification=justified, singlelinecheck=off}
\captionsetup[table]{labelsep=newline,font=footnotesize, justification=justified, singlelinecheck=off}
\usepackage{subcaption}
\usepackage{etoolbox}
\AtBeginEnvironment{table}{\sffamily}
\usepackage{booktabs,siunitx, multirow}
\usepackage{amsmath}
\usepackage{adjustbox}
\usepackage{floatrow}
\floatsetup[table]{style=Plaintop, captionskip=0pt, capposition=top}
\begin{document}
\begin{equation} \label{eq:Vpi(s)}
T = \sum_{t=0}^{M-1}f(x)
\end{equation}
\end{document}



cas-dcuses the Stix font (a Times New Roman variant), that contains the symbol in your screenshot as the sum symbol. You may be able to change that (see for example https://tex.stackexchange.com/questions/85991/how-to-change-specific-symbols-in-math-mode and https://tex.stackexchange.com/questions/14386/importing-a-single-symbol-from-a-different-font) but it is intended to be like this, if you use the class to submit to an Elsevier publication then it will be changed back to the default symbol by the publisher. – Marijn Dec 07 '20 at 18:55captionandsubcaptionwith this class, which has its own method for typesetting captions. Possiblyfloatrowis another no-go. – egreg Dec 07 '20 at 21:04