how to find the derivative of the eigenfunction?

[hechengli]

for point moment input to the structural system, usually we can use generalized moment as the input to the system, which means we need find the derivative of the eigenfuntion. how can we find the derivative of the eigenfunction if the structure is 3 dimensional?
just use diff(eigenfunction)? or use w*eigenfunction?

where I can find some reference for the calculation generalized point moment input?

Thanks

 

[MikeyP]

My intuition would be to differentiate in the direction which is normal to the axis of the moment excitation, as you are trying to find the slope of the eigenfunction which is "seen" by the moment input.

Michael