# Assertion error with MOI.initialize(d, \[:Grad\])

**URL:** <https://discourse.julialang.org/t/assertion-error-with-moi-initialize-d-grad/16796>\
**Category:** Optimization (Mathematical)\
**Created:** [October 25, 2018, 6:02pm UTC](https://discourse.julialang.org/t/assertion-error-with-moi-initialize-d-grad/16796 "2018-10-25T18:02:31Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![chkwon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chkwon/32/3632_2.png) [@chkwon](https://discourse.julialang.org/u/chkwon)\
**Post date:** [October 25, 2018, 6:02pm UTC](https://discourse.julialang.org/t/assertion-error-with-moi-initialize-d-grad/16796/1 "2018-10-25T18:02:31Z")

</div>

I’m on JuMP#v0.19-alpha.

```julia
using JuMP

plants = ["seattle", "san-diego"]
markets = ["new-york", "chicago", "topeka"]
distance = [ 2.5 1.7 1.8 ;
             2.5 1.8 1.4 ]
d = Dict()
for i in 1:length(plants), j in 1:length(markets)
    d[plants[i], markets[j]] = distance[i,j]
end

m = Model()
@variable(m, w[i in plants] >= 0)
@NLexpression(m, c[i in plants, j in markets], d[i,j] )
@NLexpression(m, profit[i in plants, j in markets], w[i] + c[i,j])
@NLconstraint(m, [i in plants, j in markets], profit[i,j] == 0)
d = JuMP.NLPEvaluator(m)
MOI.initialize(d, [:Grad])

```

This produces

```julia
**ERROR:** AssertionError: subex.linearity != CONSTANT
Stacktrace:
[1] **initialize(** ::JuMP.NLPEvaluator, ::Array{Symbol,1} **)** at **/Users/chkwon/.julia/packages/JuMP/LjMor/src/nlp.jl:372**
[2] top-level scope at **none:0**

```

How should I fix this?

---

<div class="post-metadata">

**Author:** ![miles.lubin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/miles.lubin/32/279_2.png) [@miles.lubin](https://discourse.julialang.org/u/miles.lubin)\
**Post date:** [October 26, 2018, 12:39pm UTC](https://discourse.julialang.org/t/assertion-error-with-moi-initialize-d-grad/16796/2 "2018-10-26T12:39:05Z")

</div>

Haven’t looked at it yet, but it’s clearly a bug: [Assertion error with MOI.initialize(d, [:Grad]) · Issue #1561 · jump-dev/JuMP.jl · GitHub](https://github.com/JuliaOpt/JuMP.jl/issues/1561).