Mathcad summations help

It appears that there is more to the worksheet than is shown. It's better if you upload the file, not an image.

I unfortunately cannot upload the entire file as it is quite large and there are confidentiality issues. I was hoping this was a simple fix, maybe it is not. Thanks though.

Why are there things in red? Those bits are nonfunctional, so you can't graph your function since one of its components contains an error. And what in tarnation is your independent variable? It shows up red where t2 is defined, so hf appears to not exist.

TTFN

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Offhand, I don't see anything wrong with your summations. t.2 and sigma(hf) are undefined because hf is undefined. sigma(hf) appears to be a single value, so how does it get graphed? If hf is defined as an array (like 1...5), then you have a problem because t.2 will be an array and the function sigmat(hf) will be an array and a function cannot be an array. Mixing arrays and functions is a difficulty in Mathcad. You'd be better to define everything as vectors instead of functions of hf.