I am trying to fit an Arrhenius equation to a set of data points using lsqcurvefit. I keep getting my initial guesses as the resulting parameters from the fits, but it's obviously wrong. I've used lsqcurvefit a bit, so I do not think the problem is in the syntax. I think it's in my data set. The values of my data are in the magnitude of 10^-10; it's very small. My parameters, however, are supposed to be huge. I think it's a precision thing. If I change the units for the data, the resulting parameters are supposed to increase in magnitude.
Here's what I'm doing:
Arrhenius Equation:
function [d]=Arrhenius(constant,t)
a = constant(1);
e = constant(2);
%t is inverse temp. (Kelvin): 1/T (1/Kelvin) end
Code:
x = [25+273,35+273,45+273,50+273]; %temp data
x1= 1./x; %inverse temp.
y = [0.3551 0.6390 1.4327 1.4692];
y2 = y.*10^-10 %convert to S.I. units (m^2/s)
guess = [0.002 4000]; lower = [0 100]; upper = [1 10^4];
const = lsqcurvefit(@Arrhenius,guess,x1,y2,lower,upper)
When I run this, all I get for my parameters is my initial guess, which is 0.002 and 40000. I got my initial guesses by using Mathematica, another math program, to fit the data. I really think the problem is because my y2 values are too low. Is there a way around this?
