PS Scattered Lookup Table (2D)

Approximate two-dimensional function using scattered data lookup

Since R2023a

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Libraries:
Simscape / Foundation Library / Physical Signals / Lookup Tables

Description

The PS Scattered Lookup Table (2D) block computes an approximation to some function f=f(x1,x2) given the coordinates of a scattered set of input data points in a 2D space and function values at each of these data points. The two inputs and the output are physical signals. The inputs specify the coordinates of a query point along the two directions. The output is the computed function value corresponding to the input query point.

The block computes an output value by using Delaunay triangulation to interpolate the query input value against an unstructured, or scattered, set of data points. You define the lookup table by specifying the Data points coordinate 1 parameter (vector of data point coordinates along the first direction), the Data points coordinate 2 parameter (vector of coordinates of the same data points along the second direction), and the Data points function value (vector of function values corresponding to each of these data points). All three vectors must be of the same size.

Examples

Compressor Map with Scattered Lookup

Gas flow through a compressor which is modeled using a simple controlled mass flow rate source. The compressor map that governs this mass flow rate is modeled using the PS Scattered Lookup (2D) block whose data coordinates are the pressure ratio (Pa/Pa) and the engine RPM, and the output is the mass flow rate (kg/s). The scattered lookup block performs delaunay triangulation on the input data (which is shown in plots below), and uses this to interpolate and calculate the mass flow rate based on the input. Scattered lookup allows modeling of the compressor even if the data provided is in an unstructured format.

Open Model

Ports

Input

x1 — Input query point or N-D array of query points along the first direction, untyped

physical signal

The query input value along the first direction, specified as a scalar or as an N-D array.

x2 — Input query point or N-D array of query points along the second direction, untyped

physical signal

The query input value along the second direction, specified as a scalar or as an N-D array. The signal size must match the signal size along the first direction.

Output

f — Output function value, untyped

physical signal

Output function value, based on applying the scattered lookup method to the two input values. The output signal size matches the input signal size along the first direction. The output signal unit is determined by the unit of the Data points function value parameter.

Parameters

Data points coordinate 1 — Data set of input values along the first direction

[1, 2, 3, 4, 5] 1 (default)

Data set of input values along the first direction, specified as a one-dimensional array. Specify at least three values.

Parameter unit must be commensurate with the unit of the input signal at port x1. By default, the unit is 1 (unitless). You can select a different unit from the drop-down list or type the desired unit name, such as rpm, or a valid expression, such as rad/s. For more information and a list of unit abbreviations, see How to Specify Units in Block Dialogs and Unit Definitions.

Data points coordinate 2 — Data set of input values along the second direction

[7, 6, 3, 2, 9] 1 (default)

Data set of input values along the second direction, specified as a one-dimensional array of the same size as Data points coordinate 1.

Parameter unit must be commensurate with the unit of the input signal at port x2. By default, the unit is 1 (unitless). You can select a different unit from the drop-down list or type the desired unit name, such as rpm, or a valid expression, such as rad/s. For more information and a list of unit abbreviations, see How to Specify Units in Block Dialogs and Unit Definitions.

Data points function value — Data set of function values for the lookup

[1, 2, 3, 4, 5] 1 (default)

Data set of function values for the lookup, specified as a one-dimensional array of the same size asData points coordinate 1.

Parameter unit determines the unit of the output signal at port f. By default, the unit is 1 (unitless). You can select a different unit from the drop-down list or type the desired unit name, such as rpm, or a valid expression, such as rad/s. For more information and a list of unit abbreviations, see How to Specify Units in Block Dialogs and Unit Definitions.

Extrapolation method — Select the extrapolation method

Linear (default) | Nearest

Select the approximation method for calculating the output value when the input value is outside the convex hull of the data set:

• Linear — Linear extrapolation based on boundary gradients.

• Nearest — Nearest neighbor extrapolation. This method evaluates to the value of the nearest neighbor on the boundary.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2023a