We want to optimise the truss structure subjected to one load P. The design variables are the twelve cross-sectional areas of the beams which constitute the structure.
We can formulate different single objective problems.
If we are searching a solution with minimum mass, we obtain a set of optimal design variables. If we are searching a structure with maximum stiffness (minimum compliance), we obtain a different vector of optimal design variables. One performance index corresponds to one optimal solution.