Hi, I am a beginner to the R program and am currently having some problems with the nlm function. I have already checked that my function is a positive quadratic and since it has only one turning point (i plotted the graph to check) there should be no problems in terms of finding the minimum point. However, I keep getting error messages saying : Error in nlm(poi.loglike, p = 0.3) : invalid function value in 'nlm' optimizer Why does this error message appear and what are the usual causes of this error? My primary aim is to calculate the negative poisson log likelihood function and by using the nlm function, to find the maximum likelihood estimate. Thanks to all who take their time to read and hopefully enlighten me with regards to this simple question.