Category Archives: UDFs

Digitising logarithmic scales

Posted on 16/04/2010 by dougaj4

At the suggestion of the Exceltipsmonster, I have modified the DigitGraph spreadsheet presented in the previous post to also work with logarithmic scales. Dowload the updated spreadsheet from here. The function now has two additional optional arguments, Xlog and Ylog:  =DigitGraph(Shape Name, … Continue reading →

Posted in Excel, UDFs, VBA | Tagged , , , , | 4 Comments

How to digitise a scanned image

Posted on 14/04/2010 by dougaj4

For instance, suppose we had a graph from a technical paper, and we wanted to extract numerical data from the graph lines.  One way would be to measure the points by hand and calculate the numbers by scaling from the … Continue reading →

Posted in Drawing, Excel, UDFs, VBA | Tagged , , , | 19 Comments

The Inverse Quadratic Method 3 – Brent’s Method

Posted on 13/04/2010 by dougaj4

The previous post in this series presented iterative methods to solve polynomial equations using direct or inverse quadratic interpolation.  These methods have two disadvantages: In some circumstances the function may converge very slowly, or not at all. The name of … Continue reading →

Posted in Excel, Maths, UDFs, VBA | Tagged , , , , , | 12 Comments

Calling a function as a variable

Posted on 08/04/2010 by dougaj4

The functions described in recent posts provide iterative solutions to polynomial equations, but the same method can be used for any equations that can be evaluated numerically and have a single variable.  The question then is, how can we call a … Continue reading →

Posted in Arrays, Excel, Maths, UDFs, VBA | Tagged , , , , , , | 6 Comments

The Inverse Quadratic Method – 2

Posted on 04/04/2010 by dougaj4

Firstly a clarification from the previous post in this series.  The method presented in that post was a direct application of quadratic interpolation, rather than the inverse quadratic method, as implied by the post title.  The inverse quadratic method will be … Continue reading →

Posted in Excel, Maths, UDFs, VBA | Tagged , , , , | 3 Comments