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2011 Oct 11
1
singular gradient error in nls
I am trying to fit a nonlinear regression to infiltration data in order to determine saturated hydraulic conductivity and matric pressure. The original equation can be found in Bagarello et al. 2004 SSSAJ (green-ampt equation for falling head including gravity). I am also VERY new to R and to nonlinear regressions. I have searched the posts, but am still unable to determine why my data come up with the "singular gradient" error. Here are the data: time <- c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,...