Category Archives: Curve fitting

LinEstGap with non-linear functions

Posted on March 14, 2020 by dougaj4

The LinEstGap user defined function (UDF) allows the built-in Linest function to be used on data with empty cells or hidden rows, returning results that agree with the chart trend-line function, which automatically ignores blank cells and hidden data.  It … Continue reading →

Posted in Arrays, Curve fitting, Excel, Maths, Newton, UDFs, VBA | Tagged , , , , , , , , , | 4 Comments

DigitGraph Spreadsheet and WebPlot Digitiser

Posted on March 3, 2020 by dougaj4

I have posted here previously a spreadsheet that allows XY data to be extracted from images of graphs, maps or other images of objects in a single plane: How to digitise a scanned image. I have updated the instructions for the … Continue reading →

Posted in Charts, Charts, Computing - general, Curve fitting, Drawing, Excel, UDFs, VBA | Tagged , , , , , | 5 Comments

Asymmetric Catenary Function

Posted on January 31, 2020 by dougaj4

Back in 2009, I posted a user defined function (UDF) to generate a catenary curve, that could be used together with the Excel Solver to generate a curve of a specified span and sag: A catenary function Following a discussion … Continue reading →

Posted in Coordinate Geometry, Curve fitting, Excel, Maths, Newton, UDFs, xlwings | Tagged , , , , | 1 Comment

More circle fitting options with Scipy

Posted on March 17, 2018 by dougaj4

A comment on the first post on this topic found that the method used did not work well for short arcs of large radius circles.  An example of the problem can be seen in the screen shots below: The function … Continue reading →

Posted in Coordinate Geometry, Curve fitting, Excel, Link to Python, Maths, Newton, NumPy and SciPy, UDFs, VBA, xlwings | Tagged , , , , , , , | Leave a comment

Cubic splines with jagged data

Posted on February 7, 2018 by dougaj4

A cubic spline provides a good approximation to a smooth curve, and alternative versions are available for free download (see Daily Download 22: Splines and Curves, Update to AL-Spline-Matrix, and xlwSciPy 1.09 – update for xlwings 0.10 and Scipy 0.18.1), but if … Continue reading →

Posted in Arrays, Beam Bending, Concrete, Curve fitting, Excel, Newton, UDFs, VBA | Tagged , , , , , , | 2 Comments