I received the worksheet attached to an email sent directly to me. For anyone else on this forum who wanted to interact with this question, the worksheet itself is essential. Use the green upward-pointing arrow in the toolbar to upload the worksheet.
In a private email, I corrected the issue with eval, the correction I suggested at the very beginning of this thread.
The expression to be evaluated is called f, and it contains at least five parameters such as delta, and C. The values of these parameters are read from math containers by the Evaluate-at-parameters button. However, the values are assigned to the names themselves so that it is now not possible to use these names in the eval command. My modification was to read in the values, but assign to new names such as Xdelta, and XC. Then, I removed the value command wrapped around the read statements. Finally, I adjusted the eval command to the proper syntax:
So, the code ended up looking like this:
So, this is the style in which I would have written the App. If anyone else can see a more efficient way to do all this, have at it. Perhaps we all could learn something about coding.