In call to function My_sum, the first parameter, X, should be ascending along J.
In call to function Find_val, the second parameter, Levels, should be descending along the implicit index.
You have called a function that requires the values in the array passed to the indicated parameter to be increasing along the given index, but they are not.
Suppose a function is declared as follows:
Function My_sum(X: ascending; I: Index)
Now suppose you have an array:
J ▶ 1 2 3 4 5 6 15 18 25 24 30 45
If you were to evaluate:
This error would result since the values decrease from
X[I = 3] to
X[I = 4], i.e., from 25 to 24.
The "... along the implicit index" message appears when the dimension is the implicit or null dimension, not corresponding to any index object.