> (x-1) * 10 + (y-1) + 1

Is that not equivalent to:

> (x-1) * 10 + y

or:

> x * 10 + y - 10

I agree, but I'm just now porting a program from fortran to python. They read and write files that use their own convention about indexing and values [1]

And some changes may have to been backported, and it has a lot of tricks with index of arrays of different dimensions, so I'm wrapping the formulas with +1 and -1 and hopping the best.

IIRC the python compiler does not optimize them (perhaps with numba?), but later steps in other programs are slow, so N <= 20 and whatever I do is bounded by 20^4.

[1] If the file says "1 2 7.0 \r 1 2 8.0 \r" should I keep the sum (15.0), the first (I never seen that) or the last? (Raising an error, nah.)