# Help tracking down an InexactError()

**URL:** <https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069>\
**Category:** General Usage\
**Created:** [March 30, 2018, 9:53am UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069 "2018-03-30T09:53:44Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![amrods](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/amrods/32/2543_2.png) [@amrods](https://discourse.julialang.org/u/amrods)\
**Post date:** [March 30, 2018, 9:53am UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069/1 "2018-03-30T09:53:44Z")

</div>

I’m trying to solve a dynamic programming problem and I am running into an `InexactError()` that I have not been able to track down. Can you please help me out?

```julia
const nᵢ = 2

const δ = 0.8
const σ = 1.5
const ρ = 5.0

const S = 1:3
const γc = 1.2
const πmat = [ 0.9 0.05 0.05;
                0.05 0.9 0.05;
                0.05 0.05 0.9 ]
const hi = (0.52 * γc) ^ (1 - σ) / (1 - σ)
const lo = (0.35 * γc) ^ (1 - σ) / (1 - σ)
const w = [ hi lo lo; # is
                lo hi lo ]

function J(m, y, s)
    σ / (1 - σ) * sum( ((1 - δ) * (y[i] + m[i])) ^ (1 / σ) for i in 1:nᵢ ) * m[nᵢ + 1] ^ ((σ - 1) / σ) -
    sum( m[i] * w[i, s] for i in 1:nᵢ ) + m[nᵢ + 1] * γc
end

const grid_m = 0:0.1:1.5
const grid_y′ = 0:0.1:1

using Interpolations
function interp1(S, grid_y′1, grid_y′2, Darr)
    itp = interpolate(Darr, BSpline(Cubic(Line())), OnGrid())
    sitp = scale(itp, S, grid_y′1, grid_y′2)
    return sitp
end

interp(S, grid_y′1, grid_y′2, Darr, s, y1, y2) = interp1(S, grid_y′1, grid_y′2, Darr)[s, y1, y2]

using Optim

function main()
    s = 2
    y1 = 0.0
    y2 = sqrt(abs(1.0 - y1^2.0))

    Darr = [J([1.0, 1.0, 1.0], [y1, y2], s) for s in S, y1 in grid_y′, y2 in grid_y′]

    z = x -> begin
                m1 = x[1]
                m2 = x[2]
                m3 = x[3]
                y′1 = x[4]
                y′2 = sqrt(abs(1.0 - y′1^2.0))
                return J([m1, m2, m3], [y1, y2], s) + δ * interp(S, grid_y′, grid_y′, Darr, s, y′1, y′2)
            end
        twicedif = TwiceDifferentiable(z, [0.0, 0.0, 0.0, 0.0]; autodiff = :forward)
        opt = optimize(twicedif, [1.0, 1.0, 1.0, 1.0], Newton(linesearch = LineSearches.Static()))
end

```

Running `main()` gives the error.

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<div class="post-metadata">

**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [March 30, 2018, 10:16am UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069/2 "2018-03-30T10:16:37Z")

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I think you are running into the float indices being too large to be represented in `Int64`, eg like in

```julia
julia> trunc(Int64, typemax(Int64) + 1.0)
ERROR: InexactError()
Stacktrace:
 [1] trunc(::Type{Int64}, ::Float64) at ./float.jl:672

```

It is possible that you are leaving the grid when looking for the optimum. Since B-splines don’t necessarily do well outside the grid, I would just restrict the policy choice to something sensible. Also, note that `optimize` **minimizes** , is this what you want?

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<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [March 30, 2018, 10:20am UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069/3 "2018-03-30T10:20:59Z")

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The error is thrown in `getindex` and when it happens you have `(s, y1, y2) = (2, NaN, NaN)` so I guess trying to `getindex` the return value of `interp1` with `NaN` doesn’t work so well.

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<div class="post-metadata">

**Author:** ![amrods](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/amrods/32/2543_2.png) [@amrods](https://discourse.julialang.org/u/amrods)\
**Post date:** [March 30, 2018, 10:34am UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069/4 "2018-03-30T10:34:01Z")

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Yes, I’m looking for a minimum (unfortunate and inconsistent choice of naming `optimize`, since also to obtain the results one calls `minimize` and `minimum`). Is there way to provide bounds to `optimize`?

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<div class="post-metadata">

**Author:** ![amrods](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/amrods/32/2543_2.png) [@amrods](https://discourse.julialang.org/u/amrods)\
**Post date:** [March 30, 2018, 10:35am UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069/5 "2018-03-30T10:35:47Z")

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`NaN`? When does the program go to those values?

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<div class="post-metadata">

**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [March 30, 2018, 10:49am UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069/6 "2018-03-30T10:49:30Z")

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Yes, using [box minimization](https://julianlsolvers.github.io/Optim.jl/stable/user/minimization/#box-minimization).

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<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [March 30, 2018, 10:55am UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069/7 "2018-03-30T10:55:23Z")

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I printed the values inside `interp` and that’ what they had when the error was thrown

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<div class="post-metadata">

**Author:** ![amrods](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/amrods/32/2543_2.png) [@amrods](https://discourse.julialang.org/u/amrods)\
**Post date:** [March 30, 2018, 1:01pm UTC](https://discourse.julialang.org/t/help-tracking-down-an-inexacterror/10069/8 "2018-03-30T13:01:15Z")

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So it seems that was the problem, now with constraints I obtain the solution with no problem. Thanks!