# OperatorNode¶

This is an introduction to the OperatorNode class. We write a small overarching summary of the class where we define the algorithm/equation/structure reasoning for having this class or where it fits with the rest of the code.

digraph { "MWNode" -> "FunctionNode" "MWNode" -> "OperatorNode" }
class OperatorNode : public mrcpp::MWNode<2>

Public Functions

virtual void deleteChildren() override

Recursive deallocation of children and all their descendants.

Leaves node as LeafNode and children[] as null pointer.

virtual double calcComponentNorm(int i) const override

Calculate one specific component norm of the OperatorNode (TODO: needs to be specified more).

OperatorNorms are defined as matrix 2-norms that are expensive to calculate. Thus we calculate some cheaper upper bounds for this norm for thresholding. First a simple vector norm, then a product of the 1- and infinity-norm. (TODO: needs to be more presiced).

Parameters:

i[in] TODO: deens to be specified

Eigen::MatrixXd getComponent(int i)

Matrix elements of the non-standard form.

OperatorNode is uniquely associted with a scale $$n$$ and translation $$l = -2^n + 1, \ldots, 2^n = 1$$. The non-standard form $$T_n, B_n, C_n, A_n$$ defines matrices $$\sigma_l^n, \beta_l^n, \gamma_l^n, \alpha_l^n$$ for a given pair $$(n, l)$$. One of these matrices is returned by the method according to the choice of the index parameter $$i = 0, 1, 2, 3$$, respectively. For example, $$\alpha_l^n = \text{getComponent}(3)$$.

Parameters:

i[in] Index enumerating the matrix type in the non-standard form.

Returns:

A submatrix of $$(k + 1) \times (k + 1)$$-size from the non-standard form.

Coord<D> getCenter() const

returns the coordinates of the centre of the node

Coord<D> getUpperBounds() const

returns the upper bounds of the D-interval defining the node

Coord<D> getLowerBounds() const

returns the lower bounds of the D-interval defining the node

bool hasCoord(const Coord<D> &r) const

Test if a given coordinate is within the boundaries of the node.

Parameters:

r[in] point coordinates

bool isCompatible(const MWNode<D> &node)

Testing if nodes are compatible wrt NodeIndex and Tree (order, rootScale, relPrec, etc).

bool isAncestor(const NodeIndex<D> &idx) const

Test if the node is decending from a given NodeIndex, that is, if they have overlapping support.

Parameters:

idx[in] the NodeIndex of the requested node

double getScalingNorm() const

Calculate and return the squared scaling norm.

virtual double getWaveletNorm() const

Calculate and return the squared wavelet norm.

void getCoefs(Eigen::VectorXd &c) const

wraps the MW coefficients into an eigen vector object

void printCoefs() const

Printout of node coefficients.

Returns the quadrature points in a given node.

The original quadrature points are fetched and then dilated and translated. For each cartesian direction $$\alpha = x,y,z...$$ the set of quadrature points becomes $$x^\alpha_i = 2^{-n} (x_i + l^\alpha$$. By taking all possible $$(k+1)^d$$ combinations, they will then define a d-dimensional grid of quadrature points.

Parameters:

pts[inout] quadrature points in a $$d \times (k+1)$$ matrix form.

void getPrimitiveChildPts(Eigen::MatrixXd &pts) const

Returns the quadrature points in a given node.

The original quadrature points are fetched and then dilated and translated to match the quadrature points in the children of the given node. For each cartesian direction $$\alpha = x,y,z...$$ the set of quadrature points becomes $$x^\alpha_i = 2^{-n-1} (x_i + 2 l^\alpha + t^\alpha)$$, where $$t^\alpha = 0,1$$. By taking all possible $$(k+1)^d\combinations$$, they will then define a d-dimensional grid of quadrature points for the child nodes.

Parameters:

pts[inout] quadrature points in a $$d \times (k+1)$$ matrix form.

Returns the quadrature points in a given node.

The primitive quadrature points are used to obtain a tensor-product representation collecting all $$(k+1)^d$$ vectors of quadrature points.

Parameters:

pts[inout] expanded quadrature points in a $$d \times (k+1)^d$$ matrix form.

void getExpandedChildPts(Eigen::MatrixXd &pts) const

Returns the quadrature points in a given node.

The primitive quadrature points of the children are used to obtain a tensor-product representation collecting all $$2^d (k+1)^d$$ vectors of quadrature points.

Parameters:

pts[inout] expanded quadrature points in a $$d \times 2^d(k+1)^d$$ matrix form.

void zeroCoefs()

sets all MW coefficients and the norms to zero

void setCoefBlock(int block, int block_size, const double *c)

assigns values to a block of coefficients

a block is typically containing one kind of coefficients (given scaling/wavelet in each direction). Its size is then $$(k+1)^D$$ and the index is between 0 and $$2^D-1$$.

Parameters:
• c[in] the input coefficients

• block[in] the block index

• block_size[in] size of the block

void addCoefBlock(int block, int block_size, const double *c)

adds values to a block of coefficients

a block is typically containing one kind of coefficients (given scaling/wavelet in each direction). Its size is then $$(k+1)^D$$ and the index is between 0 and $$2^D-1$$.

Parameters:
• c[in] the input coefficients

• block[in] the block index

• block_size[in] size of the block

void zeroCoefBlock(int block, int block_size)

sets values of a block of coefficients to zero

a block is typically containing one kind of coefficients (given scaling/wavelet in each direction). Its size is then $$(k+1)^D$$ and the index is between 0 and $$2^D-1$$.

Parameters:
• block[in] the block index

• block_size[in] size of the block

void attachCoefs(double *coefs)

Attach a set of coefs to this node. Only used locally (the tree is not aware of this).

void calcNorms()

Calculate and store square norm and component norms, if allocated.

void zeroNorms()

Set all norms to zero.

void clearNorms()

Set all norms to Undefined.

virtual void deleteParent()

Recursive deallocation of parent and all their forefathers.

virtual void cvTransform(int kind)

Coefficient-Value transform.

This routine transforms the scaling coefficients of the node to the function values in the corresponding quadrature roots (of its children).

NOTE: this routine assumes a 0/1 (scaling on child 0 and 1) representation, instead of s/d (scaling and wavelet).

Parameters:

operation[in] forward (coef->value) or backward (value->coef).

virtual void mwTransform(int kind)

Multiwavelet transform.

Application of the filters on one node to pass from a 0/1 (scaling on child 0 and 1) representation to an s/d (scaling and wavelet) representation. Bit manipulation is used in order to determine the correct filters and whether to apply them or just pass to the next couple of indexes. The starting coefficients are preserved until the application is terminated, then they are overwritten. With minor modifications this code can also be used for the inverse mw transform (just use the transpose filters) or for the application of an operator (using A, B, C and T parts of an operator instead of G1, G0, H1, H0). This is the version where the three directions are operated one after the other. Although this is formally faster than the other algorithm, the separation of the three dimensions prevent the possibility to use the norm of the operator in order to discard a priori negligible contributions.

Parameters:

operation[in] compression (s0,s1->s,d) or reconstruction (s,d->s0,s1).

double getNodeNorm(const NodeIndex<D> &idx) const

Gives the norm (absolute value) of the node at the given NodeIndex.

Recursive routine to find the node with a given NodeIndex. When an EndNode is found, do not generate any new node, but rather give the value of the norm assuming the function is uniformly distributed within the node.

Parameters:

idx[in] the NodeIndex of the requested node

Protected Functions

virtual void dealloc() override

Dummy deallocation of MWNode coefficients.

This is just to make sure this method never really gets called (derived classes must implement their own version). This was to avoid having pure virtual methods in the base class.

bool crop(double prec, double splitFac, bool absPrec)

Recurse down until an EndNode is found, and then crop children below the given precision threshold.

Parameters:
• prec[in] precision required

• splitFac[in] factor used in the split check (larger factor means tighter threshold for finer nodes)

• absPrec[in] flag to switch from relative (false) to absolute (true) precision.

virtual void allocCoefs(int n_blocks, int block_size)

Allocate the coefs vector.

This is only used by loose nodes, because the loose nodes are not treated by the NodeAllocator class.

virtual void freeCoefs()

Deallocate the coefs vector.

This is only used by loose nodes, because the loose nodes are not treated by the NodeAllocator class.

void setMaxSquareNorm()

recursively set maxSquaredNorm and maxWSquareNorm of parent and descendants

normalization is such that a constant function gives constant value, i.e. not same normalization as a squareNorm

void resetMaxSquareNorm()

recursively reset maxSquaredNorm and maxWSquareNorm of parent and descendants to value -1

virtual void reCompress()

Update the coefficients of the node by a mw transform of the scaling coefficients of the children.

virtual void giveChildrenCoefs(bool overwrite = true)

forward MW transform from this node to its children

it performs forward MW transform inserting the result directly in the right place for each child node. The children must already be present and its memory allocated for this to work properly.

Parameters:

overwrite[in] if true the coefficients of the children are overwritten. If false the values are summed to the already present ones.

virtual void giveChildCoefs(int cIdx, bool overwrite = true)

forward MW transform to compute scaling coefficients of a single child

it performs forward MW transform in place on a loose node. The scaling coefficients of the selected child are then copied/summed in the correct child node.

Parameters:
• cIdx[in] child index

• overwrite[in] if true the coefficients of the children are overwritten. If false the values are summed to the already present ones.

virtual void giveParentCoefs(bool overwrite = true)

backward MW transform to compute scaling/wavelet coefficients of a parent

Takes a MWParent and generates coefficients, reverse operation from giveChildrenCoefs

Warning

This routine is only used in connection with Periodic Boundary Conditions

virtual void copyCoefsFromChildren()

Copy scaling coefficients from children to parent.

Takes the scaling coefficients of the children and stores them consecutively in the corresponding block of the parent, following the usual bitwise notation.

int getChildIndex(const NodeIndex<D> &nIdx) const

Routine to find the path along the tree.

Given the translation indices at the final scale, computes the child m to be followed at the current scale in oder to get to the requested node at the final scale. The result is the index of the child needed. The index is obtained by bit manipulation of of the translation indices.

Parameters:

nIdx[in] the sought after node through its NodeIndex

int getChildIndex(const Coord<D> &r) const

Routine to find the path along the tree.

@detailsGiven a point in space, determines which child should be followed to get to the corresponding terminal node.

Parameters:

r[in] the sought after node through the coordinates of a point in space

MWNode<D> *retrieveNode(const Coord<D> &r, int depth)

Node retriever that ALWAYS returns the requested node.

Recursive routine to find and return the node with a given NodeIndex. This routine always returns the appropriate node, and will generate nodes that does not exist. Recursion starts at this node and ASSUMES the requested node is in fact decending from this node.

Parameters:
• r[in] the coordinates of a point in the node

• depth[in] the depth which one needs to descend

MWNode<D> *retrieveNode(const NodeIndex<D> &idx)

Node retriever that ALWAYS returns the requested node, possibly without coefs.

Recursive routine to find and return the node with a given NodeIndex. This routine always returns the appropriate node, and will generate nodes that does not exist. Recursion starts at this node and ASSUMES the requested node is in fact descending from this node.

Parameters:

idx[in] the NodeIndex of the requested node

MWNode<D> *retrieveParent(const NodeIndex<D> &idx)

Node retriever that ALWAYS returns the requested node.

WARNING: This routine is NOT thread safe! Must be used within omp critical.

Recursive routine to find and return the node with a given NodeIndex. This routine always returns the appropriate node, and will generate nodes that does not exist. Recursion starts at this node and ASSUMES the requested node is in fact related to this node.

Parameters:

idx[in] the NodeIndex of the requested node

const MWNode<D> *retrieveNodeNoGen(const NodeIndex<D> &idx) const

Const version of node retriever that NEVER generates.

Recursive routine to find and return the node with a given NodeIndex. This routine returns the appropriate Node, or a NULL pointer if the node does not exist, or if it is a GenNode. Recursion starts at at this node and ASSUMES the requested node is in fact decending from this node.

Parameters:

idx[in] the requested NodeIndex

MWNode<D> *retrieveNodeNoGen(const NodeIndex<D> &idx)

Node retriever that NEVER generates.

Recursive routine to find and return the node with a given NodeIndex. This routine returns the appropriate Node, or a NULL pointer if the node does not exist, or if it is a GenNode. Recursion starts at at this node and ASSUMES the requested node is in fact decending from this node.

Parameters:

idx[in] the requested NodeIndex

const MWNode<D> *retrieveNodeOrEndNode(const Coord<D> &r, int depth) const

Node retriever that returns requested Node or EndNode (const version).

Recursive routine to find and return the node given the coordinates of a point in space. This routine returns the appropriate Node, or the EndNode on the path to the requested node, and will never create or return GenNodes. Recursion starts at at this node and ASSUMES the requested node is in fact decending from this node.

Parameters:
• r[in] the coordinates of a point in the node

• depth[in] the depth which one needs to descend

MWNode<D> *retrieveNodeOrEndNode(const Coord<D> &r, int depth)

Node retriever that returns requested Node or EndNode.

Recursive routine to find and return the node given the coordinates of a point in space. This routine returns the appropriate Node, or the EndNode on the path to the requested node, and will never create or return GenNodes. Recursion starts at at this node and ASSUMES the requested node is in fact decending from this node.

Parameters:
• r[in] the coordinates of a point in the node

• depth[in] the depth which one needs to descend

const MWNode<D> *retrieveNodeOrEndNode(const NodeIndex<D> &idx) const

Node retriever that returns requested Node or EndNode (const version).

Recursive routine to find and return the node given the coordinates of a point in space. This routine returns the appropriate Node, or the EndNode on the path to the requested node, and will never create or return GenNodes. Recursion starts at at this node and ASSUMES the requested node is in fact decending from this node.

Parameters:

idx[in] the NodeIndex of the requested node

MWNode<D> *retrieveNodeOrEndNode(const NodeIndex<D> &idx)

Node retriever that returns requested Node or EndNode.

Recursive routine to find and return the node given the coordinates of a point in space. This routine returns the appropriate Node, or the EndNode on the path to the requested node, and will never create or return GenNodes. Recursion starts at at this node and ASSUMES the requested node is in fact decending from this node.

Parameters:

idx[in] the NodeIndex of the requested node

Generates scaling cofficients of children.

If the node is a leafNode, it takes the scaling&wavelet coefficients of the parent and it generates the scaling coefficients for the children

void deleteGenerated()

Deallocation of all generated nodes .

virtual std::ostream &print(std::ostream &o) const

printout ofm the node content.

Parameters:

o[in] the output stream

Protected Attributes

MWTree<D> *tree

Tree the node belongs to.

MWNode<D> *parent

Parent node.

MWNode<D> *children[1 << D]

2^D children

double squareNorm

Squared norm of all 2^D (k+1)^D coefficients.

double componentNorms[1 << D]

Squared norms of the separeted 2^D components.

double maxSquareNorm

Largest squared norm among itself and descendants.

double maxWSquareNorm

Largest wavelet squared norm among itself and descendants. NB: must be set before used.

double *coefs

the 2^D (k+1)^D MW coefficients For example, in case of a one dimensional function $$f$$ this array equals $$s_0, \ldots, s_k, d_0, \ldots, d_k$$, where scaling coefficients $$s_j = s_{jl}^n(f)$$ and wavelet coefficients $$d_j = d_{jl}^n(f)$$. Here $$n, l$$ are unique for every node.

int serialIx

index in serial Tree

int parentSerialIx

index of parent in serial Tree, or -1 for roots

int childSerialIx

index of first child in serial Tree, or -1 for leafnodes/endnodes

NodeIndex<D> nodeIndex

Scale and translation of the node.

HilbertPath<D> hilbertPath

To be documented.