I'm trying to use mathcad to do Rayleigh-Ritz approximation of the critical elastic buckling load of a joists top chord. The joists support a standing seam roof which acts to stabilize the top chord from out of plain buckling. In order to approximate the buckled shape, I chose to use a Fourier series: SUM(a

_{j}*sin(j*PI*x/L)) with j=1 to nclips. nclips is the number of roof clips along the length of the chord that is being analyzed. Ive done similar problems in a Stability of Structures class I just finished in the spring. Using mathcad to do these evaluations symbolically has been a problem since day one. I finally thought I figured out the secrets to getting an answer and not an error, but I guess I was wrong. I don't believe I've ever included a summation inside an integral though. Could this be the issue? If im defining a variable that will have variables within it, I need to call the variables as arguments, correct? This has worked for me until now. I'm trying to define a variable that has variables within it. But those variables within it come from another definition with variables within it. Mathcad doesnt seem to like this. If i use arguments in the definitions, i get an "exponent overflow" error. If i dont call arguments, i get "this value must be a scalar". also, in my summation i have a

_{j}... for the j do i use "." or "["? I am using "[" now as "." didnt work for me. Or is there some other way to do it? Thanks.

p.s. sorry if this is totally confusing. I dont know how to properly word it.