Making a fortran DLL and using it with excel has two distinct advantage.
1. We don’t need to re write the fortran code to a vb code.
2. Fortran DLL is significantly faster than the vba code.
And with all this we get goodness of excel with the power of fortran.
It is with this idea, I had created few fortran dll’s over the years and used them with excel in my professional and personal projects.
The graphics and data handling capability coupled with fortran’s numerical engine had served me well.
If you are interested in how to mesh the two, the following posts should be useful to you.