Constrained lm fit: having problem

Question

So…
Here is my problem (Using LabView 8.5) --
I want to use constrained LM routine for iterative re-convolution
fitting program (attached). I started with a simpler LM routine and it works
well. It gives correct values for one exponential decay after re-convolution
fitting.
But when I replace this with a constrained LM routine and try to run
it gives error: 
(see the second LM is replaced with constrained LM and prameter bounds are also added)
Error -20039 occurred
at NI_Gmath.lvlib:LM get new coefficients.vi
The number of columns
in the first matrix is not equal to the number of rows in the second matrix or
vector.
I’ve put in three min and max array or vector (in the lower
and upper bound of parameters).
Looking forward for help to resolve this problem.
Thanks in advance.
Attachments:
Fit_ExpDec1.vi ‏44 KB
exp_decay.vi ‏30 KB
flscn_lt_ph11.txt ‏12 KB

Answer 1

The problem is in the model function.  After the convolution the size of the output array f(x,a) is not the same as the number of data points.  This causes a series of functions to fail in the contrained LM code, yielding a very unhelpful error message far away from the error condition.  We will fix that error handling.  The unconstrained LM code does not fail, but only uses the first 750 data points (arguably a worse behavior that is harder to debug, but seems to have worked for your problem).  The fix is to modify your model function to output the same number of points as your y-data.
-Jim