function f = Fpt( fp, p )
% Fpt forces at points --> spatial/planar forces
% f=Fpt(fp,p) converts one or more linear forces fp acting at one or more
% points p to their equivalent spatial or planar forces. In 3D, fp and p
% are 3xn arrays and f is 6xn. In 2D, fp and p are 2xn and f is 3xn. In
% both cases, f(:,i) is the equivalent of fp(:,i) acting at p(:,i).
if size(fp,1)==3 % 3D forces at 3D points
f = [ cross(p,fp,1); fp ];
else % 2D forces at 2D points
f = [ p(1,:).*fp(2,:) - p(2,:).*fp(1,:); fp ];
end