# Help with a Constraint

**URL:** <https://discourse.julialang.org/t/help-with-a-constraint/13827>\
**Category:** Optimization (Mathematical)\
**Created:** [August 21, 2018, 12:46pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827 "2018-08-21T12:46:09Z")\
**Posts on this page:** 16\
**Page:** 1

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [August 21, 2018, 12:46pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/1 "2018-08-21T12:46:09Z")

</div>

Hello,

I need some help to write a constraint for my problem.  
This constraint has the following matrix:

```julia
using JuMP, CouenneNL

Nt = 2;
L = 0;
C = 0;
h = 0;
hmax = 5;
Y = zeros(Nt,Nt,hmax);
b = 2;
v = 10;

for h = 3:2:hmax
  for L = 1:Nt
    for C = 1:Nt
      Y[L,C,h] = b*h;
      b = b+1;
    end
  end
  b = 2;
end

```

But in the constraint, this matrix has to be modified a little bit. I need to insert binary variables (say `x(i=1:Nt)`) in the main diagonal (this binary variable means that if its equal `1` i’ll install certain equipment, and if it’s `0` i won’t).

To be more clear, it would be something like this:

```julia
Y = [2*h+xi*v 3*h
       4h 5*h+xi*v]

```

But i can only use this variable in the optimizaton problem, i can’t use it before.

So, we got `h = 3:2:hmax` and my constraint is something like:

```julia
m = Model()
@constraint(m,Y[:,:,h]*U[:,h] - I[:,h] == 0)

```

Where:

```julia
U is an (Nt X hmax) array, the solution of my problem
I is an (Nt X hmax) data array that was previously determined

```

How can i insert the binary variables in that constraint?

I don’t know if i made myself very clear. If you have any questions, i’ll gladly answer them.

Thanks in advance!

---

<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [August 22, 2018, 9:25am UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/2 "2018-08-22T09:25:41Z")

</div>

You can add a vector of `Nt` binary variables as:

```julia
Nt = 2
model = Model()
@variable(model, x[i=1:Nt], Bin)

```

I can’t help with the rest of your problem since I don’t know what `xi`, `U`, and `I` are.

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [August 22, 2018, 12:05pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/3 "2018-08-22T12:05:06Z")

</div>

Hello odow, thanks for your reply.

I’m sorry, that was a typo, it’s not `xi`.

It’s `x[i]`, the vector of binary variables, like you just defined. The question is, how can i add those variables in the main diagonal of my `Y` matrix in this constraint?

`@constraint(m,Y[:,:,h]*U[:,h] - I[:,h] == 0)`

`U` is the vector of the variables i wish to determinate  
`I` is a vector of data input i already have.

And i have another question… supose i have this variable `hs`:

`3 <= hs <= 25`

But `hs` can only assume odd values between those limites, i.e, `[3, 5, 7, ..., 25]`. How can this be defined?

---

<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [August 22, 2018, 10:01pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/4 "2018-08-22T22:01:36Z")

</div>

It looks like you might be new to JuMP and formulating problems as constrained optimization problems. You may want to have a read of the JuMP docs: [Quick Start Guide — JuMP -- Julia for Mathematical Optimization 0.18 documentation](http://www.juliaopt.org/JuMP.jl/0.18/quickstart.html)

There are also some example notebooks: [https://github.com/JuliaOpt/juliaopt-notebooks/tree/3110eddaf5effdecfee687739295bea05731ba33/notebooks](https://github.com/JuliaOpt/juliaopt-notebooks/tree/3110eddaf5effdecfee687739295bea05731ba33/notebooks)

> But `hs` can only assume odd values between those limites, i.e, `[3, 5, 7, ..., 25]` . How can this be defined?

You could add a dummy variable and constraint like this:

```julia
model = Model()
@variable(model, 3 <= hs <= 25, Int)
@variable(model, hs_dummy, Int)
@constraint(model, hs == 2 * hs_dummy + 1)

```

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [August 23, 2018, 10:45am UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/5 "2018-08-23T10:45:22Z")

</div>

Allright, thanks a lot for your help! Will read those links now!

I was trying work in some variables, but i got some errors:

```julia
hsmin = 3*ones(Nt,1);
hsmax = 25*ones(Nt,1);

m = Model()

@variable(m, hsmin[i] <= hs[i=1:Nt] <= hsmax[i], Int)

```

I got this error:

```julia
ERROR: LoadError: The operators <=, >=, and == can only be used to specify scalar constraints. If you are trying to add a vectorized constraint, use the element-wise
dot comparison operators (.<=, .>=, or .==) instead

```

Then i tried the element-wise comparison, like this:

```julia
hsmin = 3*ones(Nt,1);
hsmax = 25*ones(Nt,1);

m = Model()

@variable(m, hsmin[i] .<= hs[i=1:Nt] .<= hsmax[i], Int)

```

And i got this error:

`ERROR: LoadError: In @variable(m,hsmin[i] .<= hs[i = 1:Nt] .<= hsmax[i],Int): Use the form lb <= ... <= ub.`

---

<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [August 23, 2018, 10:21pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/6 "2018-08-23T22:21:51Z")

</div>

This works for me:

```julia
Nt = 3
hsmin = 3*ones(Nt,1)
hsmax = 25*ones(Nt,1)

m = Model()

@variable(m, hsmin[i] <= hs[i=1:Nt] <= hsmax[i], Int)

```

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [August 24, 2018, 1:49pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/7 "2018-08-24T13:49:39Z")

</div>

Thats weird… i tried today, and it worked. Well, moving on…

I’ve added some other variables/constraints to my problem:

```julia
using JuMP

Nt = 2;
L = 0;
C = 0;
h = 0;
hmax = 5;
Yh = zeros(Nt,Nt,hmax);
b = 2;

for h = 3:2:hmax
  for L = 1:Nt
    for C = 1:Nt
      Yh[L,C,h] = b*h;
      b = b+1;
    end
  end
  b = 2;
end

Ih = [2 1 3 4 5; 7 5 6.5 3 10];
hsmin = 3*ones(Nt,1);
hsmax = 25*ones(Nt,1);

m = Model(solver=CouenneNLSolver())

@variable(m, hsmin[i] <= hs[i=1:Nt] <= hsmax[i], Int)
@variable(m, hs_dummy[i=1:Nt], Int)
@variable(m, Vh[i = 1:Nt,h = 3:2:hmax])

@NLobjective(m, Min, sum(10*hs[i] for i = 1:Nt))
@constraint(m, hs[i=1:Nt] .== 2 * hs_dummy[i] + 1)
@constraint(m, con[i = 1:Nt,h = 3:2:hmax], Yh[i,i,h]*Vh[i,h] == Ih[i,h]) # New Constraint Added
#print(m)

status = solve(m)

println("Objective value: ", getobjectivevalue(m))
println("hs = ", getvalue(hs))
println("Vh = ", getvalue(Vh))

```

I get as result, this:

```julia
Objective value: 60.0
hs = [3.0, 3.0]
Vh = Vh: 2 dimensions:
[1,:]
  [1,3] = 0.5
  [1,5] = 0.5
[2,:]
  [2,3] = 0.43333333333333335
  [2,5] = 0.4

```

But, if i type `Vh[1,3]` in Julia, i get the following:

```julia
julia> Vh[1,3]
Vh[1,3]

```

How can i get the actual value of the `Vh[1,3]`, i.e, `0.5`? I’m asking this, because later i’ll have to solve a similar but much larger problem, and i don’t want to print all those values of `Vh` when i solve it, but would be nice to know any of them if i wish so.

---

<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [August 24, 2018, 11:25pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/8 "2018-08-24T23:25:52Z")

</div>

You have two options:

```julia
getvalue(Vh[1, 3])

```

or

```julia
Vh_solution = getvalue(Vh)
Vh_solution[1, 3]

```

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [August 27, 2018, 12:45pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/9 "2018-08-27T12:45:04Z")

</div>

Hello again, supose i have these parameters and variables:

```julia
L = 0;
C = 0;
i = 0;
Nt = 2;
hmax = 5;
@variable(model, a[i=1:Nt], Bin)
Yh = zeros(Complex128,Nt,Nt,hmax);
y1 = [0+0im 0+0im 0.05 - 0.15000im 0+0im 0.01923-0.09615im; 
      0+0im 0+0im 0.07692-0.11538im 0+0im 0.03448-0.0862im];
y2 = [0+0im 0+0im 0+6im 0+0im 0+10im; 
      0+0im 0+0im 0+6im 0+0im 0+10im];

```

Is there anyway i can write this loop as a constraint?

```julia
for h = 3:2:hmax
Yaux = zeros(Complex128,Nt,Nt,h);
  for L = 1:Nt
    for C = 1:Nt
      for i = 1:Nt
        if CONDITION 1
            if CONDITION 2
                 Yaux[L,C,h] = Yaux[L,C,h]+y1[i,h]+a[i]*y2[i,h];
            end
            if CONDITION 3
                Yaux[L,C,h] = Yaux[L,C,h]+y1[i,h];
            end
        end
        if CONDITION 4
                 Yaux[L,C,h] = Yaux[L,C,h]-y1[i,h];
                 Yaux[C,L,h] = Yaux[L,C,h];
        end
    Yh[L,C,h] = Yaux[L,C,h];
      end
    end
  end
end

```

I’ve read about the `sum()` syntax in the quick start guide, but couldn’t make it work properly. It’s not possible? or i’m doing it wrong?

---

<div class="post-metadata">

**Author:** ![joaquimg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/joaquimg/32/223_2.png) [@joaquimg](https://discourse.julialang.org/u/joaquimg)\
**Post date:** [August 27, 2018, 1:42pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/10 "2018-08-27T13:42:44Z")

</div>

If you want to construct a constraint that way you should consider using the macro `@expression` ([https://jump.readthedocs.io/en/latest/refexpr.html](https://jump.readthedocs.io/en/latest/refexpr.html)) to build a affine expression and then you can use it to create a linear constraint.  
I would also recommend using the simplest example you can here 🙂

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [August 27, 2018, 3:42pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/11 "2018-08-27T15:42:55Z")

</div>

Ok, i will look into it, thanks for the reply!

I tried adding another constraint to my problem. Like this:

```julia
using JuMP, CouenneNL

Nt = 2;
L = 0;
C = 0;
h = 0;
hmax = 5;
Yh = zeros(Nt,Nt,hmax);
b = 2;

for h = 3:2:hmax
  for L = 1:Nt
    for C = 1:Nt
      Yh[L,C,h] = b*h;
      b = b+1;
    end
  end
  b = 2;
end

Ih = [2 1 3 4 5; 7 5 6.5 3 10];
u = [10;14];
kj = 1;
Qmod = 50;
hsmin = 3*ones(Nt,1);
hsmax = 25*ones(Nt,1);

m = Model(solver=CouenneNLSolver())

@variable(m, hsmin[i] <= hs[i=1:Nt] <= hsmax[i], Int)
@variable(m, hs_dummy[i=1:Nt], Int)
@variable(m, Vh[i = 1:Nt,h = 3:2:hmax])
@variable(m, DHTv[i = 1:Nt])

@NLobjective(m, Min, sum(10*hs[i] for i = 1:Nt))

@constraint(m, hs[i = 1:Nt] .== 2 * hs_dummy[i] + 1)
@constraint(m, con[i = 1:Nt,h = 3:2:hmax], Yh[i,i,h]*Vh[i,h] == Ih[i,h])
@constraint(m, conn[i = 1:Nt, h = 3:2:hmax], DHTv[i] == sum(Vh[i,h]^2)/u[i]^2) # New Constraint added

status = solve(m)

println("Objective value: ", getobjectivevalue(m))
println("hs = ", getvalue(hs))
println("Vh = ", getvalue(Vh))
println("DHTv = ", getvalue(DHTv))

```

But i’m getting the following error:

```julia
ERROR: LoadError: AssertionError: line[1:7] == "Options"
Stacktrace:
 [1] read_sol(::IOStream, ::AmplNLWriter.AmplNLMathProgModel) at C:\Users\Muril\.julia\v0.6\AmplNLWriter\src\AmplNLWriter.jl:666
 [2] read_results(::IOStream, ::AmplNLWriter.AmplNLMathProgModel) at C:\Users\Muril\.julia\v0.6\AmplNLWriter\src\AmplNLWriter.jl:575
 [3] open(::AmplNLWriter.##117#118{AmplNLWriter.AmplNLMathProgModel}, ::String, ::String) at .\iostream.jl:152
 [4] read_results(::AmplNLWriter.AmplNLMathProgModel) at C:\Users\Muril\.julia\v0.6\AmplNLWriter\src\AmplNLWriter.jl:569
 [5] optimize!(::AmplNLWriter.AmplNLMathProgModel) at C:\Users\Muril\.julia\v0.6\AmplNLWriter\src\AmplNLWriter.jl:419
 [6] optimize!(::CouenneNL.CouenneNLNonlinearModel) at C:\Users\Muril\.julia\v0.6\Lazy\src\macros.jl:268
 [7] #solvenlp#165(::Bool, ::Function, ::JuMP.Model, ::JuMP.ProblemTraits) at C:\Users\Muril\.julia\v0.6\JuMP\src\nlp.jl:1271
 [8] (::JuMP.#kw##solvenlp)(::Array{Any,1}, ::JuMP.#solvenlp, ::JuMP.Model, ::JuMP.ProblemTraits) at .\<missing>:0
 [9] #solve#116(::Bool, ::Bool, ::Bool, ::Array{Any,1}, ::Function, ::JuMP.Model) at C:\Users\Muril\.julia\v0.6\JuMP\src\solvers.jl:172
 [10] solve(::JuMP.Model) at C:\Users\Muril\.julia\v0.6\JuMP\src\solvers.jl:150
 [11] include_string(::String, ::String) at .\loading.jl:522
 [12] include_string(::Module, ::String, ::String) at C:\Users\Muril\.julia\v0.6\Compat\src\Compat.jl:88
 [13] (::Atom.##112#116{String,String})() at C:\Users\Muril\.julia\v0.6\Atom\src\eval.jl:109
 [14] withpath(::Atom.##112#116{String,String}, ::String) at C:\Users\Muril\.julia\v0.6\CodeTools\src\utils.jl:30
 [15] withpath(::Function, ::String) at C:\Users\Muril\.julia\v0.6\Atom\src\eval.jl:38
 [16] hideprompt(::Atom.##111#115{String,String}) at C:\Users\Muril\.julia\v0.6\Atom\src\repl.jl:67
 [17] macro expansion at C:\Users\Muril\.julia\v0.6\Atom\src\eval.jl:106 [inlined]
 [18] (::Atom.##110#114{Dict{String,Any}})() at .\task.jl:80
while loading C:\Users\Muril\Desktop\Murilo\UFPE\Dissertação\Julia\Arquivos Feitos\teste_otimização_matriz_3_dimensões.jl, in expression starting on line 56

```

Does this mean that my problem is now infeasible?

I’m not worried at the moment if the problem is feasible or not, i’m just trying to learn how to write those `@variable`, `@constraint` and `@objective` macros.

Is this written correct? I mean, it would work, if the supposed infeasibility of the problem wasn’t causing the error here?

`@constraint(m, conn[i = 1:Nt, h = 3:2:hmax], DHTv[i] == sum(Vh[i,h]^2)/u[i]^2) # New Constraint added`

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [August 30, 2018, 3:13pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/12 "2018-08-30T15:13:51Z")

</div>

Well, the part above is fixed, but i ran into another problem. Heres the updated code:

```julia
using JuMP, CouenneNL

Nt = 2;
L = 0;
C = 0;
hmax = 5;
Yh = zeros(Nt,Nt,hmax);
b = 2;
Ih = [2 0 3 0 5 3 9; 7 0 6.5 0 10 4 6];
u = [10;14];
hsmin = 3*ones(Nt,1);
hsmax = 25*ones(Nt,1);

for h = 3:2:hmax
  for L = 1:Nt
    for C = 1:Nt
      Yh[L,C,h] = b*h+2.3;
      b = b+1;
    end
  end
  b = 2;
end

m = Model(solver=CouenneNLSolver())

@variable(m, a[i=1:Nt], Bin) # Not using this variable yet
@variable(m, hsmin[i] <= hs[i=1:Nt] <= hsmax[i], Int)
@variable(m, hs_dummy[i=1:Nt], Int)
@variable(m, Vh[i = 1:Nt,h = 3:2:hmax])
@variable(m, DHTv[i = 1:Nt])
@variable(m, DHIv[i = 1:Nt, h = 3:2:hmax])

@NLobjective(m, Min, sum(10*hs[i] for i = 1:Nt))

@constraint(m, hs .== 2 * hs_dummy + 1)
@constraint(m, con1[i = 1:Nt, h = 3:2:hmax], Yh[i,i,h]*Vh[i,h] == Ih[i,h])
@NLconstraint(m, con2[i = 1:Nt], DHTv[i] == sqrt(sum(Vh[i,h]^2 for h = 3:2:hmax))/u[i]^2)
@constraint(m, con3[i = 1:Nt, h = 3:2:hmax], DHIv[i,h] == Vh[i,h]/u[i]) # This constraint is causing problem

status = solve(m)

println("Objective value: ", getobjectivevalue(m))
println("hs = ", getvalue(hs))
println("Vh = ", getvalue(Vh))
println("DHTv = ", getvalue(100*DHTv))
println("DHIv = ", getvalue(DHIv))

```

If we remove the last constraint here, the code works fine. But after adding it, i got the following error:

```julia
ANALYSIS TEST: Error evaluating constraint 1: can't evaluate sqrt'(0).
WARNING: Not solved to optimality, status: Error
Objective value: NaN
WARNING: Variable value not defined for component of hs. Check that the model was properly solved.
hs = [NaN, NaN]
WARNING: Variable value not defined for Vh. Check that the model was properly solved.
Vh = Vh: 2 dimensions:
[1,:]
  [1,3] = NaN
  [1,5] = NaN
[2,:]
  [2,3] = NaN
  [2,5] = NaN
WARNING: Variable value not defined for DHTv[1]. Check that the model was properly solved.
WARNING: Variable value not defined for DHTv[2]. Check that the model was properly solved.
DHTv = [NaN, NaN]
WARNING: Variable value not defined for DHIv. Check that the model was properly solved.
DHIv = DHIv: 2 dimensions:
[1,:]
  [1,3] = NaN
  [1,5] = NaN
[2,:]
  [2,3] = NaN
  [2,5] = NaN

```

It says it cant evaluate sqrt(0) in the constraint 1. I don’t know how Couenne check those restrictions, but i assume its not by the order they are defined here? Since the first one doesn’t even have the sqrt(). And it’s a bit odd, it can’t evaluate sqrt(0).

Any ideas how to fix this?

**EDIT:** I found this in the internet:

> By default, the initial values of all the variables are zero. But to get  
> started, MINOS must compute the gradients of the constraint functions, and  
> that requires it to compute the derivative of the sqrt function at zero –  
> sqrt’(0) in the error message – which fails because that derivative of sqrt  
> at zero is infinite.

This was related to MINOS solver, but i guess the same thing happens in Couenne. Just add a really small value (1e-20 for example) to the sqrt() argument, and it should work.

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [October 16, 2018, 4:14pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/13 "2018-10-16T16:14:54Z")

</div>

Hello, i got stuck again trying to run my code, it says my problem is infeasible. So, i got two questions, if anyone could help me out.

**1st:** Imagine i got something like this:

```julia
Rmax = 3; # Rows
Cmax = 3; # Columns
hmax = 5; # Third index

```

And i got these previously calculated matrixs, say `A[R = 1:Rmax, C = 1:Cmax, h = 3:2:hmax]` and another one, say `m[R = 1:Rmax, h = 3:2:hmax]`.

Now, in my optimization problem, i need to insert some variables in the main diagonal of that matrix, to create some restrictions, so i tried this:

```julia
@variable(m, a[R=1:Rmax], Bin)
@variable(m, new_A[R = 1:Rmax, C = 1:Cmax, h = 3:2:hmax])

for h = 3:2:hmax, R = 1:Rmax, C = 1:Cmax
   if R == C
       @NLconstraint(m, new_A[R, C, h] == A[R,C,h]+a[R]*m[R,h]);
   else
       @constraint(m, new_A[R, C, h] == A[R,C,h]);
   end
end

```

**2nd** : Now, supose from those `new_A` matrixes, i need new constraints, just like in LP form `A*x = b`, so i tried this:

```julia
for h = 3:2:hmax
    @constraint(m, new_A[:,:,h]*x[:,h] .== b[:,h])
end

```

Any ideas what could be the problem here?

---

<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [October 16, 2018, 4:22pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/14 "2018-10-16T16:22:13Z")

</div>

It looks like you have a model called `m` and a matrix also called `m`.

It’s hard to say more without a small reproducible example with the actual error.

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [October 16, 2018, 4:32pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/15 "2018-10-16T16:32:48Z")

</div>

Actually, the `m` was just a random letter i put in there trying to explain, i could rename it for anything else.

I don’t know how could i put a small example here, my code is not so small and im using some .txt data and a function i created to do some calculations, so i would need to attach those also.

I’m more concerned if i’m writting those constraints in the right way (syntactically speaking), since i don’t know much about Julia and programming in general.

---

<div class="post-metadata">

**Author:** ![muriloasouza](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/muriloasouza/32/4650_2.png) [@muriloasouza](https://discourse.julialang.org/u/muriloasouza)\
**Post date:** [November 1, 2018, 1:37pm UTC](https://discourse.julialang.org/t/help-with-a-constraint/13827/16 "2018-11-01T13:37:35Z")

</div>

Hello,

I’ve tried everything i could and i still cant make it to work. If anyone has a spare time to help me out, would be awesome.

I can send you (via e-mail or something else) my model i wrote in a .pdf file, so you can understand it better and the .jl file wich i was working on, so you can see whats wrong there.

Just let me know, thanks in advance!