Not long ago, a client wanted to fit sets of data points to Weibull curves of the form:

The earlier example Find an exponential least squares fit for a set of points in Visual Basic 6 explains how to find a least squares fit for exponential data. This example uses a similar technique with the following differences:

• This example uses a different function F, error function E, and partial derivatives
• This example's functions have 4 parameters a, b, c, and d instead of just 3
• The ranges for test values of a, b, c, and d are different so they fit the data better

See the earlier example for an explanation of how this technique works.

For more information on classical Weibull functions, see:

• Weibull Distribution at Wolfram MathWorld
• Weibull distribution at Wikipedia