Fixed-Point Blockset | ![]() ![]() |
Approximate a one-dimensional function using a selected look-up method and a dynamically specified table
Library
Description
The Look-Up Table Dynamic block is a masked S-function that computes an approximation to some function y=f(x)
given x
, y
data vectors. The look-up method can use interpolation, extrapolation, or the original values of the input.
The x
data vector must be strictly monotonically increasing after conversion to the input's fixed-point data type. Note that due to quantization, the x
data vector may be strictly monotonic in doubles format, but not so after conversion to a fixed-point data type.
You define the look-up table by inputting the x
and y
table data to the block as 1-by-n vectors. To help reduce the ROM used by the code generated for this block, you can use different data types for the x
table data and the y
table data. However, these restrictions apply:
y
table data and the output vector must have the same sign, the same bias, and the same fractional slope.
x
table data and the x
data vector must have the same sign, the same bias, and the same fractional slope. Additionally, the precision and range for the x
data vector must greater than or equal to the precision and range for the x
table data.
The block generates output based on the input values using one of these methods selected from the Look-up method parameter list:
Interpolation-Extrapolation
--This is the default method; it performs linear interpolation and extrapolation of the inputs.
Interpolation-Use End Values
--This method performs linear interpolation as described above but does not extrapolate outside the end points of the input vector. Instead, the end-point values are used.
Use Input Nearest
--This method does not interpolate or extrapolate. Instead, the element in x
nearest the current input is found. The corresponding element in y
is then used as the output.
Use Input Below
--This method does not interpolate or extrapolate. Instead, the element in x
nearest and below the current input is found. The corresponding element in y
is then used as the output. If there is no element in x
below the current input, then the nearest element is found.
Use Input Above
--This method does not interpolate or extrapolate. Instead, the element in x
nearest and above the current input is found. The corresponding element in y
is then used as the output. If there is no element in x
above the current input, then the nearest element is found.
For a detailed description of all other block parameters, refer to Block Parameters.
Parameters and Dialog Box
Conversions
The table data is converted from doubles to the x
data type. This conversion is performed offline using round-to-nearest and saturation. Refer to Parameter Conversions for more information about parameter conversions.
Examples
For an example that illustrates the look-up methods supported by this block, see the example included in the Look-Up Table block reference pages.
Characteristics
Input Port(s) |
Any data type supported by the blockset |
Output Port |
Any data type supported by the blockset |
Direct Feedthrough |
Yes |
Scalar Expansion |
No |
See Also
Look-Up Table, Look-Up Table (2-D)
![]() | Look-Up Table | Look-Up Table (2-D) | ![]() |