Resolve Singularities in a Fit

Singularities in a Fit matrix indicates that there is insufficient data to properly solve the posed problem. A singular matrix means that it cannot be inverted properly, which is similar to dividing by zero in scalar problems.

The most simple case of singularities in a Fit happening occurs when there are three equations but four unknowns in algebra. This system cannot properly be solved. In a Fit, this issue is more likely to occur when the runs are not sufficiently independent, which will lead to a singular matrix.

Resolve a Fit using one of the following solutions:
  • Choose a different Fit method.
  • Modify the Fit settings.
  • Obtain additional data.

Singularities in a Fit

Consider a data set with input variables x and y, and output response z.
  • x,y,z
  • 1,2,3
  • 5,2,1
  • 6,4,4
Run 3 is a combination of runs 1 and 2 added together. The three runs would produce two pieces of information in a linear regression, which would result in a singular matrix.

It is not possible to determine which of the input variables is responsible for a change in the output response.

The conclusion is that the data set is incompatible with the Fit specification.