Question: sum with trigonometric coefficients




 I want to plot the following truncated powr series with trigonometric coefficients:


sum(-y2*y3+8*(-1)^((k-1)*(1/2))*sinh(y2*Pi*k)*sin(k*Pi*y3)/(Pi^3*k^3*cosh((1/2)*k*Pi)), k = 1 .. 10)


but I get some strange terms with a strange term "I" in it which causes strange plots. I removed and it seems ok, why does this happen and what can I do to avoid it?




best regards,



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