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...produce curve and ic50. Here is my sudo code: For (plateid in platelist) { Input data (plateid) as matrix Curve fitting model4logistic <- multdrc(rdata ~ ld, logDose=10) } The first 3 plates are ok, 4th plate has following error Error in mdrcOpt(opfct, startVec, optMethod, derFlag, constrained, warnVal, : Convergence failed I know the expected fitting is ugly, is it the reason to produce the error? Thanks you in advance for your help, Xin Gong [[alternative HTML version deleted]]