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This diagram was made for my homework of Mathematical Physics at Drexel University during my Masters education The homework assignment can be found here at http://physics.drexel.edu/~pgautam/courses/ \begin{tikzpicture} [ %decoration={ % markings, % mark=at position 1cm with {\arrow[line width=1pt]{>}}, % mark=at position .3 with {\arrow[line width=1pt]{>}}, % mark=at position .6 with {\arrow[line width=1pt]{>}}, % mark=at position 0.8 with {\arrow[line width=1pt]{>}}, % mark=at position -5mm with {\arrow[line width=1pt]{>}}, %}, on each segment/.style={ decorate, decoration={ show path construction, moveto code={}, lineto code={ \path [#1] (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast); }, curveto code={ \path [#1] (\tikzinputsegmentfirst) .. controls (\tikzinputsegmentsupporta) and (\tikzinputsegmentsupportb) .. (\tikzinputsegmentlast); }, closepath code={ \path [#1] (\tikzinputsegmentfirst) -- (\tikzinputsegmentlast); }, }, }, mid arrow/.style={ postaction={decorate, decoration={ markings, mark=at position .5 with {\arrow[#1]{stealth}} } } }, contourline/.style={line width=1.0pt}, axisline/.style={->,line width=0.3pt}, ] \tikzmath{\R=3;\r=0.5;\X=1.1*\R;\Y=1.1*\R;} \draw [axisline] (-\X,0) -- (\X,0) node [below right] {Re($z$)}; \draw [axisline] (0,1.2*\r) -- (0,-\Y) node[left] {Im($z$)}; \node at (0,0) {$\times$}; %\draw [contourline, postaction=decorate] \draw [contourline, postaction=={on each segment={mid arrow=red}}] (\r,0) node [below, font=\scriptsize] {$\epsilon$} -- (\R,0) node [above] {$R$} arc (0:-180:\R) node [above] {$-R$} -- (-\r,0) node [below, font=\scriptsize] {$-\epsilon$} arc (180:0:\r); \node at (\r,1.1*\r) {$\Gamma_{\varepsilon}$}; \node at (1.15*\R*0.7,-1.15*\R*0.7) {$\Gamma_{R}$}; % 0.7 = sin(45) = cos(45) \end{tikzpicture}

This diagram was made for my homework of Mathematical Physics at Drexel University during my Masters education The homework assignment can be found here at http://physics.drexel.edu/~pgautam/courses/ \begin{tikzpicture} [ decoration={ markings, mark=at position 0.10 with {\arrow[line width=1pt]{>}}, mark=at position 0.20 with {\arrow[line width=1pt]{>}}, mark=at position 0.30 with {\arrow[line width=1pt]{>}}, mark=at position 0.50 with {\arrow[line width=1pt]{>}}, mark=at position 0.70 with {\arrow[line width=1pt]{>}}, mark=at position 0.80 with {\arrow[line width=1pt]{>}}, mark=at position 0.90 with {\arrow[line width=1pt]{>}}, }, axes/.style={line width=0.1pt,->,opacity=.6, text opacity=1}, small/.style={font=\scriptsize} ] \tikzmath{\R=4;\r=0.7;}% Change these values to see the magic \draw [axes] (-\R*1.1,0) -- (\R*1.2,0) coordinate (xaxis) node [below] {Re$(z)$}; \draw [axes] (0,-0.1*\R) -- (0,\R*1.1) coordinate (yaxis) node [left] {Im$(z)$}; \node at (-0.5*\R,0) {$\times$}; \node at(-0.5*\R,0) [above] {$-\sigma$}; \node at (0.5*\R,0) {$\times$}; \node at (0.5*\R,0) [above] {$\sigma$}; \path [draw, line width=1.0pt, postaction=decorate] (0,0) -- (0.5*\R-\r,0) node [below,small]{$\sigma-\epsilon$} arc (180:0:\r) node [below,small]{$\sigma+\epsilon$} -- (\R,0) node [below] {$R$} arc (0:180:\R) node [below] {$-R$} -- (-0.5*\R-\r,0) node [below,small] {$-\sigma-\epsilon$} arc (180:0:\r) node [below,small] {$-\sigma + \epsilon$}-- cycle; \node at (0.5*\R,1.3*\r) {$\Gamma_{\varepsilon}$}; \node at (0.5*\R,0.8*\R) {$\Gamma_{R}$}; \end{tikzpicture}

This diagram was made for my homework of Mathematical Physics at Drexel University during my Masters education The homework assignment can be found here at http://physics.drexel.edu/~pgautam/courses/ \begin{tikzpicture} [ decoration={% markings, mark=at position 1cm with {\arrow[line width=1pt]{>}}, %mark=at position 2cm with {\arrow[line width=1pt]{>}}, mark=at position .3 with {\arrow[line width=1pt]{>}}, mark=at position .6 with {\arrow[line width=1pt]{>}}, mark=at position 0.8 with {\arrow[line width=1pt]{>}}, mark=at position -5mm with {\arrow[line width=1pt]{>}}, }, contourline/.style={line width=1.0pt}, axisline/.style={->,line width=0.3pt}, ] \draw [axisline] (-4,0) -- (4,0) coordinate (xaxis) node [below,thick] {Re($z$)}; \draw [axisline] (0,-0.6) -- (0,3.3) coordinate (yaxis) node [left,thick] {Im($z$)}; \node at (0,0) {$\times$}; \draw [contourline, postaction=decorate] (.5,0) node [below, font=\scriptsize] {$\epsilon$} -- (3,0) node [below] {$R$} arc (0:180:3) node [below] {$-R$} -- (-.5,0) node [below, font=\scriptsize] {$-\epsilon$} arc (180:0:.5); \node at (0.5,0.6) {$\Gamma_{\varepsilon}$}; \node at (2,2.6) {$\Gamma_{R}$}; \end{tikzpicture}