Symbol	Description
fi	Contact force vector applied by the i-th unit of the socket
fi,n	Normal force perpendicular to residual limb skin surface
fi,t 1	First tangential force component of the i-th unit
fi,t 2	Second tangential force component of the i-th unit
μi	Equivalent friction coefficient of the i-th unit of the socket
F max	Maximum normal contact force among all socket units
F mean	Mean normal contact force across all socket units
Var(F)	Variance of normal contact forces among socket units
G	Force transmission matrix of the socket system
Gi	Force transmission matrix of the i-th unit
Funit	System force vector composed of the output forces from all units
Wext	External load vector
Pi	Descriptive matrix of the i-th contact unit
P	Global block-diagonal descriptive matrix of all units
Φ(P)	Objective function of the pressure optimization problem
Wp	Weighting matrix for force suppression
Wi	Weighting matrix for force distribution uniformity
ΠA	Linear projection operator associated with constraints
αk	Step size at the k-th iteration of the gradient flow
i	Index of contact unit
k	Iteration index