# Plans for solvers

In order to start a solver, both a `Problem`

and `Options`

are required. Together they form a **plan** and these are stored in this folder. For sub-problems there are maybe also only `Options`

, since they than refer to the same problem.

## Options

For most algorithms a certain set of options can either be generated beforehand of the function with keywords can be used. Generally the type

`Manopt.Options`

— Type.`Options`

A general super type for all options.

**Fields**

The following fields are assumed to be default. If you use different ones, provide the access functions accordingly

`x`

an`MPoint`

with the current iterate`stop`

a`StoppingCriterion`

.

`Manopt.getOptions`

— Function.`getOptions(O)`

return the undecorated `Options`

of the (possibly) decorated `O`

. As long as your decorated options stores the options within `o.options`

and implements the `SimpleTrait`

`IsOptionsDecorator`

, this is behaviour is optained automatically.

Since the `Options`

directly relate to a solver, they are documented with the corresponding Solvers. You can always access the options (since they might be decorated) by calling `getOptions`

.

### Decorators for Options

Options can be decorated using the following trait and function to initialize

`Manopt.IsOptionsDecorator`

— Type.`IsOptionsDecorator{O}`

A trait to specify that a certain `Option`

decorates, i.e. internally stores the original `Options`

under consideration.

`Manopt.decorateOptions`

— Function.`decorateOptions(o)`

decorate the `Options`

`o`

with specific decorators.

**Optional Arguments**

optional arguments provide necessary details on the decorators. A specific one is used to activate certain decorators.

`debug`

– (`Array{Union{Symbol,DebugAction,String,Int},1}()`

) a set of symbols representing`DebugAction`

s,`Strings`

used as dividers and a subsampling integer. These are passed as a`DebugGroup`

within`:All`

to the`DebugOptions`

decorator dictionary. Only excention is`:Stop`

that is passed to`:Stop`

.`record`

– (`Array{Union{Symbol,RecordAction,Int},1}()`

) specify recordings by using`Symbol`

s or`RecordAction`

s directly. The integer can again be used for only recording every $i$th iteration.

**See also**

In general decorators often perform actions so we introduce

`Manopt.Action`

— Type.`Action`

a common `Type`

for `Actions`

that might be triggered in decoraters, for example `DebugOptions`

or `RecordOptions`

.

as well as a helper for storing values using keys, i.e.

`Manopt.StoreOptionsAction`

— Type.`StoreTupleAction <: Action`

internal storage for `Action`

s to store a tuple of fields from an `Options`

s

This functor posesses the usual interface of functions called during an iteration, i.e. acts on `(p,o,i)`

, where `p`

is a `Problem`

, `o`

is an `Options`

and `i`

is the current iteration.

**Fields**

`values`

– a dictionary to store interims values based on certain`Symbols`

`keys`

– an`NTuple`

of`Symbols`

to refer to fields of`Options`

`once`

– whether to update the internal values only once per iteration`lastStored`

– last iterate, where this`Action`

was called (to determine`once`

**Constructiors**

`StoreOptionsAction([keys=(), once=true])`

Initialize the Functor to an (empty) set of keys, where `once`

determines whether more that one update per iteration are effective

`StoreOptionsAction(keys, once=true])`

Initialize the Functor to a set of keys, where the dictionary is initialized to be empty. Further, `once`

determines whether more that one update per iteration are effective, otherwise only the first update is stored, all others are ignored.

`Manopt.getStorage`

— Function.`getStorage(a,key)`

return the internal value of the `StoreOptionsAction`

`a`

at the `Symbol`

`key`

.

`Manopt.hasStorage`

— Function.`getStorage(a,key)`

return whether the `StoreOptionsAction`

`a`

has a value stored at the `Symbol`

`key`

.

`Manopt.updateStorage!`

— Function.`updateStorage!(a,o)`

update the `StoreOptionsAction`

`a`

internal values to the ones given on the `Options`

`o`

.

`updateStorage!(a,o)`

update the `StoreOptionsAction`

`a`

internal values to the ones given in the dictionary `d`

. The values are merged, where the values from `d`

are preferred.

#### Debug Options

`Manopt.DebugAction`

— Type.`DebugAction`

A `DebugAction`

is a small functor to print/issue debug output. The usual call is given by `(p,o,i) -> s`

that performs the debug based on a `Problem`

`p`

, `Options`

`o`

and the current iterate `i`

.

By convention `i=0`

is interpreted as "For Initialization only", i.e. only debug info that prints initialization reacts, `i<0`

triggers updates of variables internally but does not trigger any output. Finally `typemin(Int)`

is used to indicate a call from `stopSolver!`

that returns true afterwards.

**Fields (assumed by subtypes to exist)**

`print`

method to perform the actual print. Can for example be set to a file export,

or to @info. The default is the `print`

function on the default `Base.stdout`

.

`Manopt.DebugChange`

— Type.`DebugChange(a,prefix,print)`

debug for the amount of change of the iterate (stored in `o.x`

of the `Options`

) during the last iteration. See `DebugEntryChange`

**Parameters**

`x0`

– an initial value to already get a Change after the first iterate. Can be left out`a`

– (`StoreOptionsAction( (:x,) )`

) – the storage of the previous action`prefix`

– (`"Last Change:"`

) prefix of the debug output`print`

– (`print`

) default method to peform the print.

`Manopt.DebugCost`

— Type.`DebugCost <: DebugAction`

print the current cost function value, see `getCost`

.

**Constructors**

`DebugCost(long,print)`

where `long`

indicated whether to print `F(x):`

(default) or `costFunction:`

`DebugCost(prefix,print)`

set a prefix manually.

`Manopt.DebugDivider`

— Type.`DebugDivider <: DebugAction`

print a small `div`

ider (default `" | "`

).

**Constructor**

`DebugDivider(div,print)`

`Manopt.DebugEntry`

— Type.`DebugEntry <: RecordAction`

print a certain fields entry of type {T} during the iterates

**Addidtional Fields**

`field`

– Symbol the entry can be accessed with within`Options`

**Constructor**

`DebugEntry(f[, prefix="$f:", print=print])`

`Manopt.DebugEntryChange`

— Type.`DebugEntryChange{T} <: DebugAction`

print a certain entries change during iterates

**Additional Fields**

`print`

– (`print`

) function to print the result`prefix`

– (`"Change of :x"`

) prefix to the print out`field`

– Symbol the field can be accessed with within`Options`

`distance`

– function (p,o,x1,x2) to compute the change/distance between two values of the entry`storage`

– a`StoreOptionsAction`

to store the previous value of`:f`

**Constructors**

`DebugEntryChange(f,d[, a, prefix, print])`

initialize the Debug to a field `f`

and a `distance`

`d`

.

`DebugEntryChange(v,f,d[, a, prefix="Change of $f:", print])`

initialize the Debug to a field `f`

and a `distance`

`d`

with initial value `v`

for the history of `o.field`

.

`Manopt.DebugEvery`

— Type.`DebugEvery <: DebugAction`

evaluate and print debug only every $i$th iteration. Otherwise no print is performed. Whether internal variables are updates is determined by `alwaysUpdate`

.

This method does not perform any print itself but relies on it's childrens print.

`Manopt.DebugGroup`

— Type.`DebugGroup <: DebugAction`

group a set of `DebugAction`

s into one action, where the internal prints are removed by default and the resulting strings are concatenated

**Constructor**

`DebugGroup(g)`

construct a group consisting of an Array of `DebugAction`

s `g`

, that are evaluated `en bloque`

; the method does not perform any print itself, but relies on the internal prints. It still concatenates the result and returns the complete string

`Manopt.DebugIterate`

— Type.`DebugIterate <: DebugAction`

debug for the current iterate (stored in `o.x`

).

**Parameters**

`long::Bool`

whether to print`x:`

or`current iterate`

`Manopt.DebugIteration`

— Type.`DebugIteration <: DebugAction`

debug for the current iteration (prefixed with `#`

)

`Manopt.DebugOptions`

— Type.`DebugOptions <: Options`

The debug options append to any options a debug functionality, i.e. they act as a decorator pattern. Internally a `Dict`

ionary is kept that stores a `DebugAction`

for several occasions using a `Symbol`

as reference. The default occasion is `:All`

and for example solvers join this field with `:Start`

, `:Step`

and `:Stop`

at the beginning, every iteration or the end of the algorithm, respectively

The original options can still be accessed using the `getOptions`

function.

**Fields (defaults in brackets)**

`options`

– the options that are extended by debug information`debugDictionary`

– a`Dict{Symbol,DebugAction}`

to keep track of Debug for different actions

**Constructors**

`DebugOptions(o,dA)`

construct debug decorated options, where `dD`

can be

- a
`DebugAction`

, then it is stored within the dictionary at`:All`

- an
`Array`

of`DebugAction`

s, then it is stored as a`debugDictionary`

within`:All`

. - a
`Dict{Symbol,DebugAction}`

. - an Array of Symbols, String and an Int for the
`DebugFactory`

`Manopt.DebugStoppingCriterion`

— Type.`DebugStoppingCriterion <: DebugAction`

print the Reason provided by the stopping criterion. Usually this should be empty, unless the algorithm stops.

`Manopt.DebugActionFactory`

— Method.`DebugActionFactory(s)`

create a `DebugAction`

where

- a
`String`

yields the correspoinding divider - a
`DebugAction`

is passed through - a [
`Symbol`

] creates`DebugEntry`

of that symbol, with the exceptions of`:Change`

,`:Iterate`

,`:Iteration`

, and`:Cost`

.

`Manopt.DebugFactory`

— Method.`DebugFactory(a)`

given an array of `Symbol`

s, `String`

s `DebugAction`

s and `Ints`

- The symbol
`:Stop`

creates an entry of to display the stoping criterion at the end (`:Stop => DebugStoppingCriterion()`

) - The symbol
`:Cost`

creates a`DebugCost`

- The symbol
`:iteration`

creates a`DebugIteration`

- The symbol
`:Change`

creates a`DebugChange`

- any other symbol creates debug output of the corresponding field in
`Options`

- any string creates a
`DebugDivider`

- any
`DebugAction`

is directly included - an Integer
`k`

introduces that debug is only printed every`k`

th iteration

see DebugSolver for details on the decorated solver.

Further specific `DebugAction`

s can be found at the specific Options.

#### Record Options

`Manopt.RecordAction`

— Type.`RecordAction`

A `RecordAction`

is a small functor to record values. The usual call is given by `(p,o,i) -> s`

that performs the record based on a `Problem`

`p`

, `Options`

`o`

and the current iterate `i`

.

By convention `i<=0`

is interpreted as "For Initialization only", i.e. only initialize internal values, but not trigger any record, the same holds for `i=typemin(Inf)`

which is used to indicate `stop`

, i.e. that the record is called from within `stopSolver!`

which returns true afterwards.

**Fields (assumed by subtypes to exist)**

`recordedValues`

an`Array`

of the recorded values.

`Manopt.RecordChange`

— Type.`RecordChange <: RecordAction`

debug for the amount of change of the iterate (stored in `o.x`

of the `Options`

) during the last iteration.

**Additional Fields**

`storage`

a`StoreOptionsAction`

to store (at least)`o.x`

to use this as the last value (to compute the change)

`Manopt.RecordCost`

— Type.`RecordCost <: RecordAction`

record the current cost function value, see `getCost`

.

`Manopt.RecordEntry`

— Type.`RecordEntry{T} <: RecordAction`

record a certain fields entry of type {T} during the iterates

**Fields**

`recordedValues`

– the recorded Iterates`field`

– Symbol the entry can be accessed with within`Options`

`Manopt.RecordEntryChange`

— Type.`RecordEntryChange{T} <: RecordAction`

record a certain entries change during iterates

**Additional Fields**

`recordedValues`

– the recorded Iterates`field`

– Symbol the field can be accessed with within`Options`

`distance`

– function (p,o,x1,x2) to compute the change/distance between two values of the entry`storage`

– a`StoreOptionsAction`

to store (at least)`getproperty(o, d.field)`

`Manopt.RecordEvery`

— Type.`RecordEvery <: RecordAction`

record only every $i$th iteration. Otherwise (optionally, but activated by default) just update internal tracking values.

This method does not perform any record itself but relies on it's childrens methods

`Manopt.RecordGroup`

— Type.`RecordGroup <: RecordAction`

group a set of `RecordAction`

s into one action, where the internal prints are removed by default and the resulting strings are concatenated

**Constructor**

`RecordGroup(g)`

construct a group consisting of an Array of `RecordAction`

s `g`

, that are recording `en bloque`

; the method does not perform any record itself, but keeps an array of records. Accessing these yields a `Tuple`

of the recorded values per iteration

`Manopt.RecordIterate`

— Type.`RecordIterate <: RecordAction`

record the iterate

**Constructors**

`RecordIterate(x0)`

initialize the iterate record array to the type of `x0`

, e.g. your initial data.

`RecordIterate(P)`

initialize the iterate record array to the data type `P`

, where `P<:MPoint`

holds.

`Manopt.RecordIteration`

— Type.`RecordIteration <: RecordAction`

record the current iteration

`Manopt.RecordOptions`

— Type.`RecordOptions <: Options`

append to any `Options`

the decorator with record functionality, Internally a `Dict`

ionary is kept that stores a `RecordAction`

for several occasions using a `Symbol`

as reference. The default occasion is `:All`

and for example solvers join this field with `:Start`

, `:Step`

and `:Stop`

at the beginning, every iteration or the end of the algorithm, respectively

The original options can still be accessed using the `getOptions`

function.

**Fields**

`options`

– the options that are extended by debug information`recordDictionary`

– a`Dict{Symbol,RecordAction}`

to keep track of all different recorded values

**Constructors**

`RecordOptions(o,dR)`

construct record decorated `Options`

, where `dR`

can be

- a
`RecordAction`

, then it is stored within the dictionary at`:All`

- an
`Array`

of`RecordAction`

s, then it is stored as a`recordDictionary`

(@ref) within the dictionary at`:All`

. - a
`Dict{Symbol,RecordAction}`

.

`Manopt.RecordActionFactory`

— Method.`RecordActionFactory(s)`

create a `RecordAction`

where

- a
`RecordAction`

is passed through - a [
`Symbol`

] creates`RecordEntry`

of that symbol, with the exceptions of`:Change`

,`:Iterate`

,`:Iteration`

, and`:Cost`

.

`Manopt.RecordFactory`

— Method.`RecordFactory(a)`

given an array of `Symbol`

s and `RecordAction`

s and `Ints`

- The symbol
`:Cost`

creates a`RecordCost`

- The symbol
`:iteration`

creates a`RecordIteration`

- The symbol
`:Change`

creates a`RecordChange`

- any other symbol creates a
`RecordEntry`

of the corresponding field in`Options`

- any
`RecordAction`

is directly included - an Integer
`k`

introduces that record is only performed every`k`

th iteration

`Manopt.getRecord`

— Function.`getRecord(o[,s=:Step])`

return the recorded values from within the `RecordOptions`

`o`

that where recorded with respect to the `Symbol s`

as an `Array`

. The default refers to any recordings during an Iteration represented by the Symbol `:Step`

`Manopt.getRecord`

— Method.`getRecord(r)`

return the recorded values stored within a `RecordAction`

`r`

.

`Manopt.hasRecord`

— Method.`hasRecord(o)`

check whether the `Options`

`o`

are decorated with `RecordOptions`

see RecordSolver for details on the decorated solver.

Further specific `RecordAction`

s can be found at the specific Options.

there's one internal helper that might be useful for you own actions, namely

`Manopt.recordOrReset!`

— Function.`recordOrReset!(r,v,i)`

either record (`i>0`

and not `Inf`

) the value `v`

within the `RecordAction`

`r`

or reset (`i<0`

) the internal storage, where `v`

has to match the internal value type of the corresponding Recordaction.

### Stepsize and Linesearch

The step size determination is implemented as a `Functor`

based on

`Manopt.Stepsize`

— Type.`Stepsize`

An abstract type for the functors representing step sizes, i.e. they are callable structurs. The naming scheme is `TypeOfStepSize`

, e.g. `ConstantStepsize`

.

Every Stepsize has to provide a constructor and its function has to have the interface `(p,o,i)`

where a `Problem`

as well as `Options`

and the current number of iterations are the arguments and returns a number, namely the stepsize to use.

**See also**

in general there are

`Manopt.ArmijoLinesearch`

— Type.`ArmijoLineseach <: Linesearch`

A functor representing Armijo line seach including the last runs state, i.e. a last step size.

**Fields**

`initialStepsize`

– (`1.0`

) and initial step size`retraction`

– (`exp`

) the rectraction used in line search`contractionFactor`

– (`0.95`

) exponent for line search reduction`sufficientDecrease`

– (`0.1`

) gain within Armijo's rule`lastStepSize`

– (`initialstepsize`

) the last step size we start the search with

**Constructor**

`ArmijoLineSearch()`

with the Fields above in their order as optional arguments.

This method returns the functor to perform Armijo line search, where two inter faces are available:

- based on a tuple
`(p,o,i)`

of a`GradientProblem`

`p`

,`Options`

`o`

and a current iterate`i`

. - with
`(M,x,F,∇Fx[,η=-∇Fx]) -> s`

where`Manifold`

`M`

, a current`MPoint`

`x`

a function`F`

, that maps from the manifold to the reals, its gradient (a`TVector`

)`∇F`

$=\nabla F(x)$ at`x`

and an optional search direction`TVector`

`η-∇F`

are the arguments.

`Manopt.ConstantStepsize`

— Type.`ConstantStepsize <: Stepsize`

A functor that always returns a fixed step size.

**Fields**

`length`

– constant value for the step size.

**Constructor**

`ConstantStepSize(s)`

initialize the stepsie to a constant `s`

`Manopt.DecreasingStepsize`

— Type.`DecreasingStepsize()`

A functor that represents several decreasing step sizes

**Fields**

`length`

– (`1`

) the initial step size $l$.`factor`

– (`1`

) a value $f$ to multiply the initial step size with every iteration`subtrahend`

– (`0`

) a value $a$ that is subtracted every iteration`exponent`

– (`1`

) a value $e$ the current iteration numbers $e$th exponential is taken of

In total the complete formulae reads for the $i$th iterate as

$ s_i = \frac{(l-i\cdot a)f^i}{i^e}$

and hence the default simplifies to just $ s_i = \frac{l}{i} $

**Constructor**

`ConstantStepSize(l,f,a,e)`

initialiszes all fields above, where none of them is mandatory.

`Manopt.Linesearch`

— Type.`Linesearch <: Stepsize`

An abstract functor to represent line search type step size deteminations, see `Stepsize`

for details. One example is the `ArmijoLinesearch`

functor.

Compared to simple step sizes, the linesearch functors provide an interface of the form `(p,o,i,η) -> s`

with an additional (but optional) fourth parameter to proviade a search direction; this should default to something reasonable, e.g. the negative gradient.

## Problems

A problem usually contains its cost function and provides and implementation to access the cost

`Manopt.Problem`

— Type.`Problem`

Specify properties (values) and related functions for computing a certain optimization problem.

`Manopt.getCost`

— Function.For any algorithm that involves a cyclic evalutaion, e.g. `cyclicProximalPoint`

, one can specify the `EvalOrder`

as

`Manopt.EvalOrder`

— Type.`EvalOrder`

type for specifying an evaluation order for any cyclicly evaluated algorithms

`Manopt.LinearEvalOrder`

— Type.`LinearEvalOrder <: EvalOrder`

evaluate in a linear order, i.e. for each cycle of length l evaluate in the order 1,2,...,l.

`Manopt.RandomEvalOrder`

— Type.`RandomEvalOrder <: EvalOrder`

choose a random order for each evaluation of the l functionals.

`Manopt.FixedRandomEvalOrder`

— Type.`FixedRandomEvalOrder <: EvalOrder`

Choose a random order once and evaluate always in this order, i.e. for l elements there is one chosen permutation used for each iteration cycle.

### Gradient based problem

`Manopt.GradientProblem`

— Type.`GradientProblem <: Problem`

specify a problem for gradient based algorithms.

**Fields**

`M`

: a manifold $\mathcal M$`costFunction`

: a function $F\colon\mathcal M\to\mathbb R$ to minimize`gradient`

: the gradient $\nabla F\colon\mathcal M \to \mathcal T\mathcal M$ of the cost function $F$

**See also**

`steepestDescent`

`GradientDescentOptions`

`Manopt.getGradient`

— Function.`getGradient(p,x)`

evaluate the gradient of a `GradientProblem`

`p`

at the `MPoint`

`x`

.

### Subgradient based problem

`Manopt.SubGradientProblem`

— Type.`SubGradientProblem <: Problem`

A structure to store information about a subgradient based optimization problem

**Fields**

`M`

– a`Manifold`

`costFunction`

– the function $F$ to be minimized`subGradient`

– a function returning a subgradient $\partial F$ of $F$

`Manopt.getSubGradient`

— Function.`getSubGradient(p,x)`

evaluate the gradient of a `SubGradientProblem`

`p`

at the `MPoint`

`x`

.

### Proximal Map(s) based problem

`Manopt.ProximalProblem`

— Type.`ProximalProblem <: Problem`

specify a problem for solvers based on the evaluation of proximal map(s).

**Fields**

`M`

- a`Manifold`

$\mathcal M$`costFunction`

- a function $F\colon\mathcal M\to\mathbb R$ to minimize`proximalMaps`

- proximal maps $\operatorname{prox}_{\lambda\varphi}\colon\mathcal M\to\mathcal M$ as functions (λ,x) -> y, i.e. the prox parameter λ also belongs to the signature of the proximal map.`numberOfProxes`

- (length(proximalMaps)) number of proxmal Maps, e.g. if one of the maps is a compined one such that the proximal Maps functions return more than one entry per function

**See also**

`Manopt.getProximalMap`

— Function.`getProximalMap(p,λ,x,i)`

evaluate the `i`

th proximal map of `ProximalProblem p`

at the point `x`

of `p.M`

with parameter `λ`

$>0$.

### Further planned problems

`Manopt.HessianProblem`

— Type.`HessianProblem <: Problem`

For now this is just a dummy problem to carry information about a Problem also providing a Hessian