# JuMP Read model from file: ERROR: LoadError: UndefVarError
**URL:** https://discourse.julialang.org/t/jump-read-model-from-file-error-loaderror-undefvarerror/102368
**Category:** Optimization (Mathematical)
**Tags:** jump
**Created:** [August 1, 2023, 7:14pm UTC](https://discourse.julialang.org/t/jump-read-model-from-file-error-loaderror-undefvarerror/102368 "2023-08-01T19:14:25Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@Stuart\_Rogers](https://discourse.julialang.org/u/Stuart_Rogers)
#### Post date: [August 1, 2023, 7:14pm UTC](https://discourse.julialang.org/t/jump-read-model-from-file-error-loaderror-undefvarerror/102368/1 "2023-08-01T19:14:26Z")
I use JuMP to solve a simple MILP read in from the input file test.mps. After solving the model, JuMP generates an undefined variable error when I try to access the value of a variable in the MILP.
test.mps:
NAME
ROWS
N OBJ
G c1
G c2
COLUMNS
x c1 6
x c2 7
x OBJ 12
MARKER ‘MARKER’ ‘INTORG’
y c1 8
y c2 12
y OBJ 20
RHS
rhs c1 100
rhs c2 120
RANGES
BOUNDS
LO bounds x 0
PL bounds x
LO bounds y 0
UP bounds y 3
ENDATA
Code in Wotan\_read.jl:
using JuMP
using COPT
#using HiGHS
model = read\_from\_file(“test.mps”)
opt = COPT.Optimizer
#opt = HiGHS.Optimizer
#relax\_integrality(model)
set\_optimizer(model,opt)
print(model)
optimize!(model)
@show termination\_status(model)
@show primal\_status(model)
@show dual\_status(model)
@show objective\_value(model)
@show value(x)
@show value(y)
@show shadow\_price(c1)
@show shadow\_price(c2
Output:
$ julia Wotan\_read.jl
Cardinal Optimizer v6.5.7. Build date Jul 28 2023
Copyright Cardinal Operations 2023. All Rights Reserved
Setting parameter ‘LogToConsole’ to 1
Min 12 x + 20 y
Subject to
c1 : 6 x + 8 y ≥ 100
c2 : 7 x + 12 y ≥ 120
x ≥ 0
y ∈ [0, 3]
y integer
Model fingerprint: ed27c8a2
Using Cardinal Optimizer v6.5.7 on Linux
Hardware has 24 cores and 48 threads. Using instruction set X86\_NATIVE (1)
Minimizing a MIP problem
The original problem has:
2 rows, 2 columns and 4 non-zero elements
1 integers
Presolving the problem
The presolved problem has:
2 rows, 2 columns and 4 non-zero elements
1 integers
Starting the MIP solver with 32 threads and 64 tasks
```
Nodes Active LPit/n IntInf BestBound BestSolution Gap Time
0 1 -- 0 1.520000e+02 -- Inf 0.00s
```
H 0 1 – 0 1.520000e+02 2.657143e+02 42.8% 0.00s
H 0 1 – 0 1.520000e+02 2.051429e+02 25.9% 0.01s
0 1 – 1 2.050000e+02 2.051429e+02 0.07% 0.01s
1 0 0.0 1 2.051429e+02 2.051429e+02 0.00% 0.01s
1 0 0.0 1 2.051429e+02 2.051429e+02 0.00% 0.01s
Best solution : 205.142857143
Best bound : 205.142857143
Best gap : 0.0000%
Solve time : 0.01
Solve node : 1
MIP status : solved
Solution status : integer optimal (relative gap limit 0.0001)
Violations : absolute relative
bounds : 0 0
rows : 0 0
integrality : 0
termination\_status(model) = MathOptInterface.OPTIMAL
primal\_status(model) = MathOptInterface.FEASIBLE\_POINT
dual\_status(model) = MathOptInterface.NO\_SOLUTION
objective\_value(model) = 205.14285714285714
ERROR: LoadError: UndefVarError: `x` not defined
Stacktrace:
[1] top-level scope
@ show.jl:1128
in expression starting at /home/stuart/julia\_code/Wotan/Wotan\_read.jl:21
---
### Author:  [@odow](https://discourse.julialang.org/u/odow)
#### Post date: [August 1, 2023, 9:50pm UTC](https://discourse.julialang.org/t/jump-read-model-from-file-error-loaderror-undefvarerror/102368/2 "2023-08-01T21:50:24Z")
This is expected.
Here, `value(x)` refers to the Julia binding `x`, not the “x” variable inside the model. There is no binding `x` in the current scope, so you get the `UndefVarError`.
You need something like `x = variable_by_name(model, "x")`. See the docs [JuMP · JuMP](https://jump.dev/JuMP.jl/stable/api/JuMP/#variable_by_name)
See also the note in [Models · JuMP](https://jump.dev/JuMP.jl/stable/manual/models/#Read-a-model-from-file)