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Error -20041 (the Input Matrix is Singular) When Setting Initial Guess Coefficient with Nonlinear Curve Fit VI

Updated May 11, 2023

Reported In

Software

  • LabVIEW Full

Issue Details

The "Nonlinear Curve Fit .vi" returns an error when I change the Initial Guess Coefficients. The default coefficients (2, 0, 4) work as expected. However, when I change the values to my own input, I get Error -20041. How do I set my initial guess coefficients?

Solution

The Lev-Mar algorithm is an iterative process and depends heavily on the initial guess coefficients.
To establish a best initial guess, use the following equation:

y = a * exp(b * x) + c
  1. Guess "c" by looking at the smallest data point.
  2. Guess "a" by plugging the y-intercept into the equation.
  3. Calculate "b" by substituting a known (x,y) point and guesses of "a" and "c" into the equation.

Additional Information

A matrix is singular if and only if the determinant is 0. This error is likely returned due to the rounding of floating point numbers during the iterative calculation.

Related Links

Nonlinear Curve Fit VI

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