As I understand, it is an optimization problem. LeastSquare=sum[y-f(x)]^2 Minimize least square by solving equations about a, b, and c. An iterative method could be developed to get the result or some R functions might be found useful. Please refer http://r.789695.n4.nabble.com/Is-there-any-Gauss-newton-library-function-in-R-td897353.html Hope it helps. -- View this message in context: http://r.789695.n4.nabble.com/help-needed-in-least-square-curve-fit-equation-tp4666504p4666655.html Sent from the R help mailing list archive at Nabble.com.