Global Fitting in indirectly coupled systems
blgreene87
I am trying to model a set of time dependent data using four states that can interconvert through well known pathways, i.e. a -> b, b -> c but c cannot directly go to a. I have the four data sets and would like to fit them globally to this model, but I am a little confused about how to do this. The global fitting seems to work well when you have very similar functional forms for each species, but what if you don't? Since the states are all not directly connected, and the state diagram of the four would look like a tripod with one state in the middle mitigating all others, each one state is typically described by a single exponential, but the middle state is described by three. I want a single exponential to connect two states (i.e. be global for those two) but be local in the whole data set. I guess the other way to do it would be to have the rate of the exponential be global and the amplitude be local for all and thus it could be zero for the states that don't fit this exponential, but that just doesn't seem very elegant. Any suggestions?
I am pretty new to Igor, so sorry if this is a little naive, but I appreciate the help.
Are you able to describe your system in simple, easy-to-read terms? Can you write down some equations?
Setting the amplitude of an exponential fit function won't work- it will result in no dependence on the decay constant for that exponential term, and therefor a zero derivative in the Hessian matrix, resulting in a singular matrix error.
John Weeks
WaveMetrics, Inc.
support@wavemetrics.com
August 7, 2014 at 01:45 pm - Permalink