Index in position 1 is invalid. Array indices must be positive integers or logical values.

I am a python programmer and new to Matlab. Therefore, facing some basic issues. Please help me out with this. I am pasting my code here.

Error Message:

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in spectrum_uncompressed (line 30)
X_per_bartlett = Px(x_sig_with_noise_updated, 1);

load('lowpasssignal.mat')
%check for mean
mn = dsp.Mean;
x_sig_with_noise_mean = mn(x_sig_and_noise);
 
%new signal definition with mean
 
x_sig_with_noise_updated = x_sig_and_noise - x_sig_with_noise_mean;
 
%Periodogram on x to compute PSD
N = length(x_sig_with_noise_updated);
X_per = periodo(x_sig_with_noise_updated, N);
 
 
fs = 2*pi; %sampling of 2*pi becuase signal is complex valued
    
freq_0 = 0:fs/length(x_sig_with_noise_updated):fs - fs/N;
figure()
 
plot(freq_0/pi, X_per)
hold on
grid on
title('Periodogram Using FFT')
xlabel('Normalized Frequency (\times\pi rad/sample)')
ylabel('Power/Frequency')
 
%Bartlett's method
 
X_per_bartlett = Px(x_sig_with_noise_updated, 1, 1, N);
freq_1 = 0:fs/length(X_per_bartlett):fs;
freq_1_updated = freq_1(1:length(freq_1)-1);
plot(freq_1_updated/pi, X_per_bartlett)
hold on
grid on
title('Periodogram Using Bartlett Avg')
xlabel('Normalized Frequency (\times\pi rad/sample)')
ylabel('Power/Frequency')

The functions are here:

%periodo

function perx = periodo(x, N)
  
        x_fft = fft(x);
        perx = (1/(2 * pi * N)) * abs(x_fft) .^ 2
    
end

%Bartlett

function per_x = Px(x, win, n1, n2)
    x = x(:);
    if nargin == 2
        n1 = 1; n2 = length(x); 
        display(n1, n2);
    end;
    N = n2 - n1 + 1
    w = ones(N, 1);
    if (win == 1) w = bartlett(N);
    elseif (win == 2) w = hamming(N);
    end;
    
    xw = x(n1:n2).*w/norm(w);
    per_x = N * periodogram(xw);

[Stephen23]

@Tworit Kumar Dash: Please show us the complete error mesage. This means all of the red text. We cannot guess where your error occurs and we do not have your data to run your code with.

[Tworit Kumar Dash]

@Stephen Cobeldick, I have updated the question with the error code.

[madhan ravi]

upload .mat file

[Tworit Kumar Dash]

Added the mat file.

[Walter Roberson]

I do not see the .mat file?

Answer 1

[Walter Roberson]

somehow you have aa variable in your workspace that is named Px so matlab thinks you are indexing instead of calling a function .

[Tworit Kumar Dash]

I think I just solved it by renaming Px to some other name. What do you mean by a workspace here, because on my main program, I don't see any Px only except for the function call.

[Walter Roberson]

Your code is not a function, so if you were to do

Px = 'hello';

before running the code then Px would be considered to be a variable instead of a function. You might have assigned something to Px in an earlier version of the code and not cleared your variables since then. Using functions instead of scripts protects against this kind of accidental use of left-over variables.

Also you are using load() without assigning the output to a variable. If you happened to have a variable named Px in the .mat file, the stored value would become active. It is recommended that you assign load() to a variable and access the structure, something like

filestruct = load('lowpasssignal.mat');
dsp = filestruct.dsp;   %pull out the specific variable you need from the structure.

[Evelyn Cooper]

Thank you so much! This helped me figure out/debug why tf wasn't working for me.

Answer 2

[madhan ravi]

x=1:5 %an example to make you understand
x(1)
x(0)  %this will throw the same error as you have