"This variable is undefined" bug in Mathcad Prime 8

[Kristian]

I recently went from Mathcad Prime version 5 to 8, and now I often see errors like "This variable is undefined", where a variable seems to be undefined.

However, if I put the Symbolic Evaluation arrow in the line with the definition of f(t) in the first line, the "This variable is undefined" error disappears, and I can plot the function and so on.

Can anyone please tell me what is going on? 

I teach engineering math, and my students are getting more and more frustrated about Mathcad Prime

[Werner_E · Accepted solution]

Can you post the worksheet?!

When I retype your expressions (in Prime 9), no error occurs.

Chances are that when you edit an expression a few times or copy part of it from somewhere else, the labelling of variables may change.

So check, if ALL occurrences of the variable "n" (also the one under sum symbol) are labelled the very same. After retyping your expressions these are all labelled as "(-)" (meaning automatic). If one of them is labelled as "(variable)" this will throw the error. If all are labelled as "(variable)" Prime would be happy as well.
Its annoying but auto-labelling does not work that well in Prime and ever so often you have to re-label variables manually.

[Kristian]

Hi Werner

Thanks! Changing the n variable under the sum did the work.

Super annoying and very unintuitive error.

[LucMeekes]

Super annoying, and counter-intuitive, I agree.

But it helps a lot if you change the font/appearance of each of the different labels.

I use:

which has the added benefit that units are displayed as they should, according to ISO 80000.

Success!

Luc

[ttokoro]

RMS value.