x=-pi/2:pi/200:pi/2;
y=abs(sin(x));
plot(x,y,'k-');
set(gcf,'color','white');
hold on
xx=-pi/2:pi/100:pi/2;
yy=abs(sin(xx));
xx1=[xx;xx;0*xx;1./(0*xx)];
xx1=(reshape(xx1,4*max(size(xx1)),1))';
yy1=[0*yy;yy;yy;1./(0*xx) ];
yy1=(reshape(yy1,4*max(size(yy1)),1))';
zzz=line(xx1,yy1);
set(zzz,'color',[0.5 0.5 0.5],'linestyle',':') 
hold off 
set(gca,'ylim',[0 1.08],'xlim',[-1.65 1.65])