# Introduction to RipQP

## Input

Here is a basic example:

``````using QuadraticModels, LinearAlgebra, SparseMatricesCOO
Q = [6. 2. 1.
2. 5. 2.
1. 2. 4.]
c = [-8.; -3; -3]
A = [1. 0. 1.
0. 2. 1.]
b = [0.; 3]
l = [-1.0;0;0]
u = [Inf; Inf; Inf]
c,
SparseMatrixCOO(tril(Q)),
A=SparseMatrixCOO(A),
lcon=b,
ucon=b,
lvar=l,
uvar=u,
c0=0.,
name="QM"
)``````
``````QuadraticModels.QuadraticModel{Float64, Vector{Float64}, SparseMatricesCOO.SparseMatrixCOO{Float64, Int64}, SparseMatricesCOO.SparseMatrixCOO{Float64, Int64}}
Problem name: QM
All variables: ████████████████████ 3      All constraints: ████████████████████ 2
free: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 free: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
lower: ████████████████████ 3                lower: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
upper: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                upper: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
low/upp: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0              low/upp: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
fixed: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                fixed: ████████████████████ 2
infeas: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0               infeas: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
nnzh: (  0.00% sparsity)   6               linear: ████████████████████ 2
nonlinear: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
nnzj: ( 33.33% sparsity)   4

Counters:
obj: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 grad: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 cons: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
cons_lin: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0             cons_nln: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 jcon: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jgrad: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                  jac: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0              jac_lin: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jac_nln: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                jprod: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0            jprod_lin: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jprod_nln: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0               jtprod: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0           jtprod_lin: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jtprod_nln: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 hess: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                hprod: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jhess: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0               jhprod: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0``````

Once your `QuadraticModel` is loaded, you can simply solve it RipQP:

``````using RipQP
stats = ripqp(QM)
println(stats)``````
``````Generic Execution stats
status: first-order stationary
objective value: 1.1250000001819647
primal feasibility: 5.253818735984856e-13
dual feasibility: 4.5240388878182354e-11
solution: [-6.602556960437742e-11  1.499999999967075  6.550018773077893e-11]
multipliers: [-5.000000000443094  2.249999999907261]
multipliers_L: [1.3498983056074131e-12  9.350004367856938e-13  2.7500000006802963]
multipliers_U: [0.0  0.0  0.0]
iterations: 5
elapsed time: 7.794533014297485
solver specific:
iters_sp: 5
pdd: 1.002449365261327e-10
psoperations: ∅
iters_sp3: 0
iters_sp2: 0
relative_iter_cnt: 20``````

The `stats` output is a GenericExecutionStats.

``````using QPSReader, QuadraticModels
``````QuadraticModels.QuadraticModel{Float64, Vector{Float64}, SparseMatricesCOO.SparseMatrixCOO{Float64, Int64}, SparseMatricesCOO.SparseMatrixCOO{Float64, Int64}}
Problem name: Generic
All variables: ████████████████████ 32     All constraints: ████████████████████ 27
free: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 free: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
lower: ████████████████████ 32               lower: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
upper: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                upper: ███████████████⋅⋅⋅⋅⋅ 19
low/upp: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0              low/upp: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
fixed: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                fixed: ██████⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 8
infeas: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0               infeas: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
nnzh: ( 98.86% sparsity)   6               linear: ████████████████████ 27
nonlinear: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
nnzj: ( 90.39% sparsity)   83

Counters:
obj: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 grad: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 cons: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
cons_lin: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0             cons_nln: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 jcon: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jgrad: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                  jac: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0              jac_lin: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jac_nln: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                jprod: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0            jprod_lin: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jprod_nln: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0               jtprod: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0           jtprod_lin: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jtprod_nln: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                 hess: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0                hprod: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0
jhess: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0               jhprod: ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅ 0``````

## Logging

RipQP displays some logs at each iterate.

``stats = ripqp(QM)``
``"Execution stats: first-order stationary"``

You can deactivate logging with

``stats = ripqp(QM, display = false)``
``"Execution stats: first-order stationary"``

It is also possible to get a history of several quantities such as the primal and dual residuals and the relative primal-dual gap. These quantites are available in the dictionary `solver_specific` of the `stats`.

``````stats = ripqp(QM, history = true)
pddH = stats.solver_specific[:pddH];``````

## Change configuration and tolerances

You can use `RipQP` without scaling with:

``stats = ripqp(QM, scaling = false)``
``"Execution stats: first-order stationary"``

You can also change the `RipQP.InputTol` type to change the tolerances for the stopping criteria:

``stats = ripqp(QM, itol = InputTol(max_iter = 100, ϵ_rb = 1e-4), scaling = false)``
``"Execution stats: first-order stationary"``

## Save the Interior-Point system

At every iteration, RipQP solves two linear systems with the default Predictor-Corrector method (the affine system and the corrector-centering system), or one linear system with the Infeasible Path-Following method.

To save these systems, you can use:

``````w = SystemWrite(write = true, name="test_", kfirst = 4, kgap=3)
stats1 = ripqp(QM, w = w)``````
``"Execution stats: first-order stationary"``

This will save one matrix and the associated two right hand sides of the PC method every three iterations starting at iteration four. Then, you can read the saved files with:

``````using DelimitedFiles, MatrixMarket

## Timers

You can see the elapsed time with:

``stats1.elapsed_time``
``0.12202596664428711``

For more advance timers you can use TimerOutputs.jl:

``````using TimerOutputs
TimerOutputs.enable_debug_timings(RipQP)
reset_timer!(RipQP.to)
stats = ripqp(QM)
TimerOutputs.complement!(RipQP.to) # print complement of timed sections
show(RipQP.to, sortby = :firstexec)``````
``````──────────────────────────────────────────────────────────────────────
Time                    Allocations
───────────────────────   ────────────────────────
Tot / % measured:       259ms /   0.0%           22.6MiB /   0.0%

Section     ncalls     time    %tot     avg     alloc    %tot      avg
──────────────────────────────────────────────────────────────────────
factorize       10   38.8μs  100.0%  3.88μs     0.00B     - %    0.00B
──────────────────────────────────────────────────────────────────────``````