fitting sum of two decaying exponentials (over damped oscillator)

five-parameter fit to the equation A*exp(-t/T1) + B*exp( -t/T2 ) + offset

[A, B, T1, T2, offset, Ssq] = fit_overdamping( t, y, options )
fitting overdamped harmonic oscillator of the form
y(t) = A exp( -t/T1 ) + B exp( -t/T2) + offset
where A and B are the amplitudes (assumed positive), and T1, T2 are the
decay times. Ssq is the sum of residuals.

options are 'notify' to show progress and 'plot' to give a plot
you can also supply a guess or series of guesses via a row vector or
matrix, m, where size( m, 2 ) = 5;

if you just run program without arguments it will do an example

examples are
fit_overdamping( t, y, 'notify', 'plot')
[A, B, T1, T2, offset] = fit_overdamping( t, y, [1 2 3 4 5])

Note: this script uses LMFnlsq from MATLAB central file exchange
[e-mail] 2/8/12