restart: y_exact:=rhs(dsolve({epsilon*diff(y(x),x$2)+diff(y(x),x)+exp(-x),y(0)=0,y(1)=1},y(x))); y_approx:=exp(-x)+(2-exp(-1))*(1-exp(-x/epsilon))-1; plot([subs(epsilon=0.01,y_exact),subs(epsilon=0.01,y_approx)],x=0..1,color=[blue,red]); plot(subs(epsilon=0.01,y_exact-y_approx),x=0..1); JSFH

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