# IOTA Whitepaper Math Section 4.1: Am I calculating this right?

I'm trying to craft an example going through the math equation in Section 4.1 . I'm trying to show my work. Can you tell me if I've got it right and if not, help correct me? Hx – Cumulative weight at node x – Let’s say 65
Hy – Cumulative weight at node y – Let’s say 70
Hz – Cumulative weight at node z – Let’s say 75
α – Try with 1
Pxy = exp( -1( 65 – 70 ) * ((75+74+…65)^(-1(65 – 75)) )^-1
Pxy = exp( 5) * (770^10))^-1
Pxy = 1.365e-29^5
Pxy = 4.737e-145

Unfortunately, this doesn't look correct. Regardless of the actual numbers, you are not treating the sum as a sum but rather as a single summand. On top of that, you seem to be missing the `exp` function in a few places during your `P_xy` calculation.

Below I am pasting a sample calculation for a transaction `x` that is referenced by three other transactions `y_1`,`y_2`,`y_3`. That is, `y_i⇝x` for `i=1,2,3`.

So for example, the transition probability of going from `x` to `y_3` is ≈ 32%. • Am I not iterating over y as well? To go from z to x I have to pass through y (75, 74, 73, 72, 72, 71, 70!!!,..) Are you saying this Sigma is not Sigma notation? home.windstream.net/okrebs/page136.html – Bill Bisco Jan 16 '18 at 14:30
• Is the math supposed to be 75^( -1(65 - 75) + 74^(-1(65 - 75) .... ? – Bill Bisco Jan 16 '18 at 14:32
• I mean, generally, there are several issues. For one, the cum weight of `x` should be larger than the one of `y`. Secondly, neither `((75+74+…65)^(-1(65 – 75)))^-1` nor `75^( -1(65 - 75) + 74^(-1(65 - 75)` has the `exp` function in it, so I am really not sure what you are calculating. – Phil-ZXX Jan 16 '18 at 15:28
• The whitepaper says put random particles on sites on the tangle and have them walk towards the target. The walkers are defined as y approves x so so site x is somewhere earlier in the tangle and site y is a tip at the end? The tip should have a larger weight than a previous transaction earlier no? x should smaller than y no? – Bill Bisco Jan 16 '18 at 16:31
• 6exp( 3 ) is the same as 6^3 or 6*6*6 or 216 no? In my comment above I said z is 75 and I start the sigma with 75 that should be 75 ^ ( -1 ( 65 - 75) and then I add that to the next right 74 ^ (-1 (65 - 75) ? – Bill Bisco Jan 16 '18 at 16:34