The deflection is ‘δ’, strain energy ‘U’ and load ‘W’ on a truss. These are related by
1
\({\rm{\delta }} = \frac{{\partial {\rm{U}}}}{{\partial {\rm{W}}}}\)
2
\({\rm{\delta }} = \frac{{{\partial ^2}{\rm{U}}}}{{\partial {{\rm{W}}^2}}}\)
3
\({\rm{\delta }} = \frac{{{\partial ^3}{\rm{U}}}}{{\partial {{\rm{W}}^3}}}\)
4
\({\rm{\delta }} = {\left( {\frac{{\partial {\rm{U}}}}{{\partial {\rm{W}}}}} \right)^2}\)
5
\({\rm{\delta }} = \frac{{\partial {\rm{^4U}}}}{{\partial {\rm{W^4}}}}\)