# Non linear model fit [duplicate]

I need to fit this, but for some reason I cannot...

data = {{0.617,0.8}, {0.605,0.6}, {0.5997,0.4}, {0.5972,0.2}, {0.5985,0.1}}; soln = NonlinearModelFit[data, {y - 2478.82*wlog[kc + 1]}, {y,w,k}, {c}, MaxIterations -> 1000]

I appreciate any help...Thanks!

• Undefined function wlog? wlog= w Log? Space between k and c in kc? Commented Oct 30, 2014 at 6:23
• You are attempting to estimate 4 parameters (y, w, k, and the error variance) with just 5 data points. You've got to be kidding! You need more data or a much, much simpler model or tell whoever has asked you to do this that it shouldn't be done.
– JimB
Commented Dec 12, 2016 at 3:56

After fixing the many typos you have (what is log? Mathematica uses Log), and adding a constraint on k else complex solution will result, here it is

data = {{0.617, 0.8}, {0.605, 0.6}, {0.5997, 0.4}, {0.5972, 0.2}, {0.5985, 0.1}};
soln = NonlinearModelFit[data, {y - 2478.82*w Log[k c + 1], k > 0},
{y, w, k}, c, MaxIterations -> 1000]


There is still some warning about converge and the tolerance. You can play with options to try to eliminate these.