kill(all);

dim:[ri=10.5, rm=11.5, ro=15.5, dr=0.03, E= 210000];

coeff: (ro^2+rm^2)/(ro^2-rm^2)+(rm^2+ri^2)/(rm^2-ri^2);

pf: E*dr/rm/coeff;

ev([coeff, pf], dim);