\documentclass[border=3pt]{standalone}

\usepackage[OT1]{fontenc}
\renewcommand*\familydefault{\sfdefault}

\usepackage{ifthen}
\usepackage{tikz}
\usetikzlibrary[
    arrows,
    arrows.meta,
    calc,
    shadings,
    decorations.pathmorphing,
    decorations.markings
]

\begin{document}

\begin{tikzpicture}
  [x=1.0cm, y=1.5cm]
  
  \foreach \ii in {-1,...,1}{
    \ifthenelse{\isodd{\ii}}{
      \draw[line width=1pt, red] (\ii, 0) -- ++(0, 0.4);
    }{
      \ifthenelse{\ii = 0}{
        \draw[line width=1pt,dashed, blue] (\ii, 0) -- ++(0,-0.4);
      }{
        \draw[line width=1pt,blue] (\ii, 0) -- ++(0,-0.4);
      } 
    }
  }
  \draw[{Stealth[length=3pt]}-{Stealth[length=3pt]}] (-1.8, 0) -- (1.8, 0);
  \node[below right] at (0,0) {\scriptsize 0};

  \begin{scope}[shift={(4, 0)}]
  \node[below right] at (0,0) {\scriptsize 0};
  \foreach \ii in {-1,...,1}{
    \ifthenelse{\isodd{\ii}}{
      \draw[line width=1pt, red] (\ii, 0) -- ++(0, 0.4);
      \begin{scope}[shift={(\ii, 0)}]
        \shade[draw=blue, line width=0.4pt, bottom color=blue, top color=white]
            (-0.5, 0) -- 
            plot [samples=400, domain=-0.5:0.5]
            (\x, {-0.4*exp(-\x*\x / 0.01)})
            (0.5, 0);
      \end{scope}
    }{
      \ifthenelse{\ii = 0}{
        \draw[line width=1pt,dashed, blue] (\ii, 0) -- ++(0,-0.4);
      }{
        \draw[line width=1pt,blue] (\ii, 0) -- ++(0,-0.4);
        \begin{scope}[shift={(\ii, 0)}]
          \shade[draw=red, line width=0.4pt, bottom color=white, top color=red]
              (-0.5, 0) -- 
              plot [samples=400, domain=-0.5:0.5]
              (\x, {0.4*exp(-\x*\x / 0.01)})
              (0.5, 0);
        \end{scope}
      }
    }
  }
  \draw[{Stealth[length=3pt]}-{Stealth[length=3pt]}] (-1.8, 0) -- (1.8, 0);
  \node[below=3pt] at (0, -0.4) {\footnotesize (a)};
  \end{scope}

  \begin{scope}[shift={(8.5, 0.75)}]
  \node[above] at (0,0) {\scriptsize 0};
  \foreach \ii in {-1,...,1}{
    \ifthenelse{\isodd{\ii}}{
      \begin{scope}[shift={(\ii, 0)}]
        \shade[draw=red, line width=0.4pt, bottom color=white, top color=red]
            (-0.5, 0) -- 
            plot [samples=400, domain=-0.5:0.5]
            (\x, {0.4*exp(-\x*\x / 0.01)})
            (0.5, 0);
      \end{scope}
    }{
      \begin{scope}[shift={(\ii, 0)}]
        \shade[draw=blue, line width=0.4pt, bottom color=blue, top color=white]
            (-0.5, 0) -- 
            plot [samples=400, domain=-0.5:0.5]
            (\x, {-0.4*exp(-\x*\x / 0.01)})
            (0.5, 0);
      \end{scope}
    }
  }
  \draw[{Stealth[length=3pt]}-{Stealth[length=3pt]}] (-1.8, 0) -- (1.8, 0);
  \node[below=3pt] at (0, -0.4) {\footnotesize (b)};
  \end{scope}

  \begin{scope}[shift={(8.5,-0.75)}]
  \node[below] at (0,0) {\scriptsize 0};
  \shade[draw=red, line width=0.4pt, bottom color=white, top color=red]
      (-0.5, 0) -- 
      plot [samples=400, domain=-0.5:0.5]
      (\x, {0.4*exp(-\x*\x / 0.01)})
      (0.5, 0);
  \draw[{Stealth[length=3pt]}-{Stealth[length=3pt]}] (-1.8, 0) -- (1.8, 0);
  \node[below=3pt] at (0, -0.4) {\footnotesize (c)};
  \end{scope}
  \node[] at (2, 0) {$=$};
  \node[] at (6, 0) {$+$};


\end{tikzpicture}

\end{document}
