Off[General::precw];​​a=b=1/Sqrt[3];
p[r_]:=
;
l[r_]:=Re[Tr[Chop[MatrixPower[p[r].p[r],1/2]]]]-1;​​​​Plot[l[r],{r,0,0.2}]​​​​ListLinePlot[Table[Chop[N[l[r]]],{r,1/100,80/100,1/100}],PlotRange{0,0.5},DataRange{1/100,80/100},RotateLabelFalse,FrameStyleDirective[Black,12],FrameTrue,FrameStyleDirective[Black,12],FrameLabel{Style["r",13,Bold,Black],Style["N",13,Bold,Black]},PlotStyle{Dashing[Block],Black},PlotLabelStyle["b",13,Bold,Black],PlotRangeAll]