# Equality constrain to NLopt
**URL:** https://discourse.julialang.org/t/equality-constrain-to-nlopt/101852
**Category:** Optimization (Mathematical)
**Tags:** question
**Created:** [July 20, 2023, 7:56pm UTC](https://discourse.julialang.org/t/equality-constrain-to-nlopt/101852 "2023-07-20T19:56:59Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@mary](https://discourse.julialang.org/u/mary)
#### Post date: [July 20, 2023, 7:56pm UTC](https://discourse.julialang.org/t/equality-constrain-to-nlopt/101852/1 "2023-07-20T19:56:59Z")
Hi, I am doing topology optimization. I have seen some tutorials. I want to add volume constrain to my model as below:
```julia
v/v0=f
```
which v is material volume and v0 is domain volume and f is volume fraction.
could you please tell me how can i add this to my code
```julia
using NLopt
function gf_p_optimize(p_init; r, β, η, TOL = 1e-6, MAX_ITER = 700, fem_params)
##################### Optimize #################
opt = Opt(:LD_CCSAQ, fem_params.np)
opt.lower_bounds = 0
opt.upper_bounds = 1
opt.ftol_rel = TOL
opt.maxeval = MAX_ITER
opt.min_objective = (p0, grad) -> gf_p(p0, grad; r, β, η, fem_params)
(g_opt, p_opt, ret) = optimize(opt, p_init)
@show numevals = opt.numevals # the number of function evaluations
return g_opt, p_opt
end
```
thank you
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [July 20, 2023, 8:19pm UTC](https://discourse.julialang.org/t/equality-constrain-to-nlopt/101852/2 "2023-07-20T20:19:39Z")
CCSAQ doesn’t support equality constraints — the CCSA algorithm requires the feasible set to have a non-empty interior in general.
Normally if you are doing structural optimization you can replace volume constraints with an inequality constraint V ≤ f V\_0, since the optimization naturally “wants” the structure to use as much material as possible (i.e. the constraint will be active at the optimum, so you will end up with V = f V\_0).
---
### Author:  [@mary](https://discourse.julialang.org/u/mary)
#### Post date: [July 20, 2023, 8:44pm UTC](https://discourse.julialang.org/t/equality-constrain-to-nlopt/101852/3 "2023-07-20T20:44:54Z")
so it should be work by adding
```julia
inequality_constraint!(opt, sum(p0) - 0.4*fem_params.np<0)
```
what if i dont implement constrain in my model?