Documentation

PS Lookup Table (1D)

Approximate one-dimensional function using specified lookup method

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

Description

The PS Lookup Table (1D) block computes an approximation to some function f=f(x) given data vectors x and f. Both the input and the output are physical signals.

The length of the x and f data vectors provided to this block must match. Also, the x data vector must be strictly monotonic, either increasing or decreasing.

You define the lookup table by specifying the Table grid vector parameter as a 1-by-n vector (x data vector) and the Table values parameter as a 1-by-n vector (f data vector). The block generates output based on the input values using the selected interpolation and extrapolation methods. You have a choice of two interpolation methods and two extrapolation methods. You also have an option for the block to issue an error if the input signal value is outside the table grid vector range.

Plotting Table Data

Plotting a lookup table lets you visualize the data before simulating the model, to make sure that the table is correct. The plot reflects tabulated data specified for the block, as well as the selected interpolation and extrapolation options.

To plot the data, right-click the block in your model and, from the context menu, select Foundation Library > Plot Table. For more information, see Plot Lookup Tables.

Ports

Input

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Input value along the x-axis.

Output

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Output function value, based on applying the lookup table to the input value.

Parameters

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Specify the vector of input values as a one-dimensional array. The input values vector must be strictly monotonic, either increasing or decreasing. The values can be nonuniformly spaced. For smooth interpolation, the vector must contain at least three values. For linear interpolation, two values are sufficient.

Specify the vector of output values as a one-dimensional array. The output values vector must be of the same size as the input values vector.

Select one of the following interpolation methods for approximating the output value when the input value is between two consecutive grid points:

  • Linear — Uses a linear function. Select this option to get the best performance.

  • Smooth — Uses a modified Akima interpolation algorithm. For details, see tablelookup. Select this option to produce a continuous curve with continuous first-order derivatives.

Select one of the following extrapolation methods for determining the output value when the input value is outside the range specified in the argument list:

  • Linear — Extends from the edge of the interpolation region linearly. The slope of the linear extrapolation is equal to the slope of the interpolated curve at the edge of the interpolation region.

  • Nearest — Extends from the edge of the interpolation region as a constant. The value of the nearest extrapolation is equal to the value of the interpolated curve at the edge of the interpolation region. Select this option to produce an extrapolation that does not go above the highest point in the data or below the lowest point in the data.

  • Error — Issues an error if the input signal is outside the range of the table. Select this option to avoid going into the extrapolation mode when you want your data to be within the table range.

Introduced in R2007a

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