# Inaccurate values generated by loop compared to hand calculations. Can't find my mistake

**URL:** <https://discourse.julialang.org/t/inaccurate-values-generated-by-loop-compared-to-hand-calculations-cant-find-my-mistake/64060>\
**Category:** New to Julia\
**Created:** [July 5, 2021, 3:30am UTC](https://discourse.julialang.org/t/inaccurate-values-generated-by-loop-compared-to-hand-calculations-cant-find-my-mistake/64060 "2021-07-05T03:30:16Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Mark\_Williams](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mark_williams/32/7668_2.png) [@Mark\_Williams](https://discourse.julialang.org/u/Mark_Williams)\
**Post date:** [July 5, 2021, 3:30am UTC](https://discourse.julialang.org/t/inaccurate-values-generated-by-loop-compared-to-hand-calculations-cant-find-my-mistake/64060/1 "2021-07-05T03:30:16Z")

</div>

Firstly, I apologise for asking what looks like such a silly question. Any help will be very welcome. I have a function which uses a double loop to compute the entries of a matrix `L`. I know the matrix values from a paper I’m reading but I can’t seem to match them. As a first step to figuring out the problem I hand computed, then wrote a function to calculate the first entry and got exactly what I wanted.

Somehow, in moving to the function that calculates the whole matrix I’ve made a mistake. Unfortunately I don’t see where it is. The value I’m expecting is 0.002073 but what I calculate in `find_L` is 0.002512. The relative difference is big and throws off the rest of my code. The function is

```julia
using Parameters
using QuantEcon
using DelimitedFiles

Model = @with_kw (ef = readdlm("eff.txt"),
                  s_prob = readdlm("prob.txt"),
                  init_dist = readdlm("init_dist.txt"),
                  mc = tauchen(9, 0.96, sqrt(0.045), 0, 2),
                  P = mc.p,
                  states = mc.state_values,
                  work = 40,
                  T = 60,
                  )

m = Model();

function find_L(m)
    @unpack P, ef, states, init_dist, work, hbar, s_prob = m
    ϕ = zeros(work, length(states))
    ϕ[1,:] = init_dist
    
    for t in 2:work
        ϕ[t,:] = transpose(P)*ϕ[t-1,:]*s_prob[t]
    end

    L = zeros(work, length(states))
    for t in 1:work
        for i in 1:length(states)
            L[t,i] = exp(states[i])*ef[t]*ϕ[t,i]
        end
    end
    
    return L
end

```

As a minimum working example to calculate the first entry

```julia
using QuantEcon
mc = tauchen(9, 0.96, sqrt(0.045), 0, 2)
P = mc.p
states = mc.state_values
                  

ef = 0.599232388
s_prob = 1
states = -1.515228816828316
init_dist = 0.0157471 
 
function first(ef, s_prob, states, P, init_dist)
    ϕ = init_dist
    x = exp(states)*ef*ϕ
    return x
end
first(ef, s_prob, states, P, init_dist) = 0.002073673367670175

```

which is exactly correct. It would be helpful for me to make the function for the full matrix operational but unfortunately it includes data drawn from .txt files and I wasn’t sure how to include those in my question. I should also mention that I know the \phi matrix is correct (in any case the first element of the matrix `L` doesn’t depend on anything I’ve calculated).

---

<div class="post-metadata">

**Author:** ![cvanaret](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cvanaret/32/11594_2.png) [@cvanaret](https://discourse.julialang.org/u/cvanaret)\
**Post date:** [July 5, 2021, 6:41am UTC](https://discourse.julialang.org/t/inaccurate-values-generated-by-loop-compared-to-hand-calculations-cant-find-my-mistake/64060/3 "2021-07-05T06:41:42Z")

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Try this in your first code:

```julia
L = zeros(work, length(states))
    for t in 1:work
        for i in 1:length(states)
            if t == 1 && i == 1
                println("L[1, 1] = ", exp(states[i]), " * ", ef[t], " * ", ϕ[t,i])
            end
            L[t,i] = exp(states[i])*ef[t]*ϕ[t,i]
        end
    end

```

and compare with your second code.