How to use the root command in a program

You've probably run into the automatic labelling trap of Mathcad Prime:

Notice that my cursor (short vertical blue line) is on the T.b[0 variable where it is assigned the value of T.b.B0 (of which I could not find a definition, so that may be yet another problem). The label (see the ribbon: 'Labels', 3rd from top-right) of this T.b[0 variable is 'Variable'. If you move the cursor to the offending item T.b[i-1 inside the argument list of the root function you see that the label of that item is not 'Variable', but '(-)'. Now both items refer to an element of the vector T.b (the first to its element with index 0, the other to the element with index i-1. The labels are different, so the arrays are different, and that's not your intent, I guess. You can correct this by manually changing the label of T.b[i-1 to be a 'variable' as well. then this problem should be out of the way.

Unfortunately I cannot do it, because I'm limited to Prime Express (no programming or solve blocks allowed). But if you (still) run into more issues, don't hesitate to come back here.

Success!
Luc