fixpt_look1_func_plot

Plot fixed-point approximation function for lookup table

Syntax

fixpt_look1_func_plot(xdata,ydata,'func',... xmin,xmax,xdt,xscale,ydt,yscale,rndmeth) errworst= fixpt_look1_func_plot(xdata,ydata,'func',... xmin,xmax,xdt,xscale,ydt,yscale,rndmeth)

Description

fixpt_look1_func_plot(xdata,ydata,'func',... xmin,xmax,xdt,xscale,ydt,yscale,rndmeth)plots a lookup table approximation function and the error from the ideal function.

errworst= fixpt_look1_func_plot(xdata,ydata,'func',... xmin,xmax,xdt,xscale,ydt,yscale,rndmeth)plots a lookup table approximation function and the error from the ideal function. The outputerrworstis the maximum absolute error.

You can usefixpt_look1_func_approxto generatexdata和ydata，分别为查找表的断点和表数据。fixpt_look1_func_approxapplies the ideal function to the breakpoints inxdatato produceydata. While this method is the easiest way to generateydata, you can choose other values forydataas input forfixpt_look1_func_plot. Choosing different values forydatacan, in some cases, produce a lookup table with a smaller maximum absolute error.

Input Arguments

xdata

Vector of breakpoints for the lookup table.

ydata

Vector of values from applying the ideal function to the breakpoints.

func

功能x为此近似断点。将此表达式包装在单引号中'sin(2*pi*x)'.

xmin

Minimum value ofx.

xmax

Maximum value ofx.

xdt

Data type ofx.

xscale

Scaling for thexvalues.

ydt

Data type ofy.

yscale

Scaling for theyvalues.

rndmeth

Rounding mode supported by fixed-point Simulink^®块：

`'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'`	在零方向上圆形到最近的代表数。

Examples

Plot a fixed-point approximation of the sine function using data points generated byfixpt_look1_func_approx:

func = 'sin(2*pi*x)'; % Define the range over which to optimize breakpoints xmin = 0; xmax = 0.25; % Define the data type and scaling for the inputs xdt = ufix(16); xscale = 2^-16; % Define the data type and scaling for the outputs ydt = sfix(16); yscale = 2^-14; % Specify the rounding method rndmeth = 'Floor'; % Define the maximum acceptable error errmax = 2^-10; % Choose even, power-of-2 spacing for breakpoints spacing = 'pow2'; % Generate data points for the lookup table [xdata,ydata,errworst]=fixpt_look1_func_approx(func,... xmin,xmax,xdt,xscale,ydt,yscale,rndmeth,errmax,[],spacing); % Plot the sine function (ideal and fixed-point) & errors fixpt_look1_func_plot(xdata,ydata,func,xmin,xmax,... xdt,xscale,ydt,yscale,rndmeth);

fixpt_look1_func_plotplots the fixed-point sine function, using generated data points, and plots the error between the ideal function and the fixed-point function. The maximum absolute error and the number of points required appear on the plot. The error drops to zero at a breakpoint, but increases between breakpoints due to curvature differences between the ideal function and the line drawn between breakpoints.

The lookup table requires 33 points to achieve a maximum absolute error of2^-11.3922.

Documentation

fixpt_look1_func_plot

Syntax

Description

Input Arguments

Examples

See Also

Topics

在R2006a之前引入

Simulink Documentation

万博1manbetx

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