Accelerating the pace of engineering and science

# Documentation Center

• Trial Software

# fixpt_interp1

Implement 1-D lookup table

## Syntax

y = fixpt_interp1(xdata,ydata,x,xdt,xscale,ydt,yscale,rndmeth)

## Description

y = fixpt_interp1(xdata,ydata,x,xdt,xscale,ydt,yscale,rndmeth) implements a one-dimensional lookup table to find output y for input x. If x falls between two xdata values (breakpoints), y is the result of interpolating between the corresponding ydata values. If x is greater than the maximum value in xdata, y is the maximum ydata value. If x is less than the minimum value in xdata, y is the minimum ydata value.

If the input data type xdt or the output data type ydt is floating point, fixpt_interp1 performs the interpolation using floating-point calculations. Otherwise, fixpt_interp1 uses integer-only calculations. These calculations handle the input scaling xscale and the output scaling yscale and obey the rounding method rndmeth.

## Input Arguments

xdata

Vector of breakpoints for the lookup table, such as linspace(0,8,33).

ydata

Vector of table data that correspond to the breakpoints for the lookup table, such as sin(xdata).

x

Vector of input values for the lookup table to process, such as linspace(-1,9,201).

xdt

Data type of input x, such as sfix(8).

xscale

Scaling for input x, such as 2^-3.

ydt

Data type of output y, such as sfix(16).

yscale

Scaling for output y, such as 2^-14.

rndmeth

Rounding mode supported by fixed-point Simulink® blocks:

 'Ceiling' Round to the nearest representable number in the direction of positive infinity. 'Floor' (default) Round to the nearest representable number in the direction of negative infinity. 'Nearest' Round to the nearest representable number. 'Toward Zero' Round to the nearest representable number in the direction of zero.

## Examples

Interpolate outputs for x using a 1-D lookup table that approximates the sine function:

xdata = linspace(0,8,33).';
ydata = sin(xdata);
% Define input x as a vector of 201 evenly
% spaced points between -1 and 9 (includes
% values both lower and higher than the range
% of breakpoints in xdata)
x = linspace(-1,9,201).';
% Interpolate output values for x
y = fixpt_interp1(xdata,ydata,x,sfix(8),2^-3,sfix(16),...
2^-14,'Floor')