I need to fit an exponential curve through a given dataset. The curve is defined by: $y=A\exp(Bx)$ so I need to estimate $A$ and $B$.
However my $y$ values are all negative. I tried using Least squares fitting as described here The problem I have is the fact that the formula uses $\ln(y)$ which returns NaN for a negative value.
How do I get around this problem?
Can someone recommend a good source to read about this fitting approach?
In advance thank you for your help.
If $y$ values are all negative, $-y$ values are all positive. Just handle the problem of $$-y=-A \exp(Bx)$$
$$\ln(-y) = Bx+\ln(-A)$$