Hi everyone, I'm having a bit of difficulty choosing an admissible function for a fixed-fixed nonuniform bar. I chose the function φ(x) = 1 - cos(2πx/L). But when solving for the the stiffness and mass coefficients: kij = ∫EA(x)φiφjdx mij = ∫ρ(x)φiφjdx, I am not sure where I should have the "i" and "j" in my function. In an example for a fixed-free beam, the function that was given was: φ(x) = sin(πx/2L), which was changed to φi(x) = sin[((2i-1)πx)/2L]. Should I choose my function to be φi(x) = 1 - cos(2πix/L)? And why?