Common Terms

Intel® oneAPI Math Kernel Library (oneMKL) - Data Parallel C++ Developer Reference

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Date 12/16/2022

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Common Terms

Glossary
Mathematical Notation in the Data Fitting Component
Hints in the Data Fitting Component
Boundary Condition Types

Glossary

Assume we need to interpolate a function f(x) on the [a, b) interval using splines.

Let’s break [a, b) into sub-intervals by n points called partition points or simply partition. Function values at these points () are also given.

Spline has k degree if it can be expressed by the following polynomial:

Splines are constructed on sub-intervals. So, for each sub-interval there are following polynomials:

are called spline coefficients.

Function is interpolated at points of [a, b). Such points are called interpolation sites or simply sites. Sites might or migtn’t equals to partition points.

Mathematical Notation in the Data Fitting Component

Concept	Mathematical Notation
Partition	, where ..
Uniform partition	Partition which meets the following condition:
Quasi-uniform partition	Partition which meets the constraint with a constant `C` defined as: , where , ,
Vector-valued function of dimension `p` being fit	.
A `k`-order derivative of function `f(x)` at point `t`	.
Function `p` agrees with function `f` at the points .	For every point in sequence that occurs `m` times, the equality holds for all .
The `k`-th divided difference of function `f` at points . This difference is the leading coefficient of the polynomial of order `k+1` that agrees with `f` at .	. In particular, , .

Hints in the Data Fitting Component

The Intel® oneAPI Math Kernel Library (oneMKL) Data Fitting component provides ways to specify some “hints” for partitions, function values, coefficients, interpolation sites.

Partition Hints

The following are supported:

Non-uniform.

Quasi-uniform.

Uniform.

Syntax

enum class partition_hint {
  non_uniform,
  quasi_uniform,
  uniform
};

Function Values Hints

Let is a partition, is a vector-valued function. Function values are stored in the one-dimensional array with nx * ny elements. 2 different layouts are possible: row major and column major.

For row major layout function values are stored as the following:

Let is the function value that corresponds to the i-th partition point and the j-th function.
For column major:

Let is the function value that corresponds to the i-th partition point and the j-th function.

The following hints are supported:

Row major.

Column major.

Syntax

enum class function_hint {
  row_major,
  col_major
};

Coefficients Hints

Let is a partition, is a vector-valued function. Let cubic spline should be constructed. It means that it requires 4 coefficients per each interpolation interval and function value. Cofficients are stored in the one-dimensional array with 4 * (nx - 1) * ny elements.

For row major:

Let is the coefficient value that corresponds to the i-th partition point, the j-th function.
For column major:

Let is the coefficient value that corresponds to the i-th partition point, the j-th function.

The following is supported:

row major

Syntax

enum class coefficient_hint {
  row_major
};

Sites Hints

The following are supported:

Non-uniform.

Uniform.

Sorted.

Syntax

enum class site_hint {
  non_uniform,
  uniform,
  sorted
};

Interpolation Results Hints

Let is a vector-valued function, are sites, d is a number of derivatives (including interpolation values) that needs to be calculated. So, size of memory to store interpolation results is nsite * ny * d elements.

6 different layouts are possible:

functions-sites-derivatives

Let is an interpolation result that corresponds to the i-th site, the j-th function, the k-th derivative.

functions-derivatives-sites

Let is an interpolation result that corresponds to the i-th site, the j-th function, the k-th derivative.

sites-functions-derivatives

Let is an interpolation result that corresponds to the i-th site, the j-th function, the k-th derivative.

sites-derivatives-functions

Let is an interpolation result that corresponds to the i-th site, the j-th function, the k-th derivative.

derivatives-functions-sites

Let is an interpolation result that corresponds to the i-th site, the j-th function, the k-th derivative.

derivatives-sites-functions

Let is an interpolation result that corresponds to the i-th site, the j-th function, the k-th derivative.

The following are supported:

functions-sites-derivatives

functions-derivatives-sites

sites-functions-derivatives

sites-derivatives-functions

Syntax

enum class interpolate_hint {
  funcs_sites_ders,
  funcs_ders_sites,
  sites_funcs_ders,
  sites_ders_funcs
};

Derivatives Hints

Following hints are added to choose which derivtive orders need to be computed during the interpolate function:

just compute interpolation values

compute first derivative of the spline polynomial only

compute second derivative of the spline polynomial only

compute third derivative of the spline polynomial only

Syntax

enum class derivatives {
  zero,
  first,
  second,
  third
};

operator| is overloaded to create combinations of derivative orders to be computed by interpolate.

Example

Assume that interpolation values, 1-st and 3-rd derivatives need to be computed. To create a bit mask that is passed to interpolate it needs following:

std::bitset<32> bit_mask = derivatives::zero | derivatives::first | derivatives::third;

Boundary Condition Types

Some type of splines requires boundary conditions to be set. The following types are supported:

Free end ().

Periodic.

First derivative.

Second Derivative.

Syntax

enum class bc_type {
  free_end,
  first_left_der,
  first_right_der,
  second_left_der,
  second_right_der,
  periodic
};

NOTE:

First derivative and second derivative types must be set on the left and on the right borders.
Free end doesn’t require any values to be set.

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Intel® oneAPI Math Kernel Library (oneMKL) - Data Parallel C++ Developer Reference

Common Terms

Glossary

Mathematical Notation in the Data Fitting Component

Hints in the Data Fitting Component

Boundary Condition Types