Why is it showing an "Unrecognized function or variable 'sample'" error code?

Question

Zachary Oliver 2020-4-2

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/514738-why-is-it-showing-an-unrecognized-function-or-variable-sample-error-code

回答： sugga singh 2021-2-28

%Sample and Alias 2

clear
clc
close all
% Define Sampling Frequencies to be Observed
Fs = [8000, 5000, 4000, 3300, 3000, 2700];
%% Create Array Ts such that Ts = 1 / Fs
Ts = [1/8000, 1/5000, 1/4000, 1/3300, 1/3000, 1/2700];
%Number of Frequency Copies (Must be Odd)
freq_copies = 9;
%Titles of Figures
graph_title = ["Fs = 8000 Hz";"Fs = 5000 Hz";"Fs = 4000 Hz";...
                "Fs = 3300 Hz";"Fs = 3000 Hz";"Fs = 2700 Hz"];
%% Generate For Loop Code
% This for loop loops through 6 different sampling frequencies and plots
% the fft spectrum of each time sequency. It then creates a 2x3 subplot 
% of the different fft spectrums
for k = 1:6
    
    %Create 2D array, x, of size [N, K] where N is the number of points in a
    %specific time sequence and K is the kth sample rate
    %In other words, every column of x is a different sampled version of
    %x(t) with a different sample rate
    k
    x(:,k)=sample(Ts(k));
    %Take FFT of kth x_n and then create freq_copies number of copies label
    %this variable (copied version of fft(x)) X
    X(:,k)=repmat(abs(fftshift(fft(x(:,k)))),freq_copies,1);
    %Create indexed frequency variable for x axis of plot (given)
    f(:,k) = -(freq_copies)*Fs(k)/2:(freq_copies)*Fs(k)/(length(X(:,k))-1):(freq_copies)*Fs(k)/2;
    
    %Generate subplot entry for each result
    subplot(2,3,k)
    %plot the kth column of f vs the kth column of X
    plot(f(:,k),X(:,k));
    %set x limits to make plot more clear
    xlim([-6000 6000])
    %Label Axis
    xlabel('Frequency (Hz)')
    ylabel('|X(f)|');
    %Title graph with kth value in graph_title
    title(graph_title(k))
end

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Joe Privacy 2021-2-27

编辑：Joe Privacy 2021-2-27

xlim([-6000 6000]) is wrong. Sampling frequency dictates that your max fft frequency is 4000, or else you'll have aliasing problems.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2020-4-2

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/514738-why-is-it-showing-an-unrecognized-function-or-variable-sample-error-code#answer_423469

在 MATLAB Online 中打开

MATLAB does not define any function named sample

Note that Ts(k) is a scalar, so you would be calling sample() passing in just a scalar, so it is not clear what you are sampling.

Question:

% Define Sampling Frequencies to be Observed
Fs = [8000, 5000, 4000, 3300, 3000, 2700];
%% Create Array Ts such that Ts = 1 / Fs
Ts = [1/8000, 1/5000, 1/4000, 1/3300, 1/3000, 1/2700];

Wouldn't it be safer to define Ts = 1./Fs; ?