Add a decade plots to graph

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monkey_matlab 2015-9-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/239309-add-a-decade-plots-to-graph

Sim_Noise_Data.txt

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From the attached simulated data file, I wanted to add decade plots as follows:

30 dB per decade from 100 to 3000
20 dB per decade from 3000 to 1000000
Horizontal line from 1000000 to 40000000

Here is my code for the original data file:
% Select file
clear;
clc;
[FileName,PathName] = uigetfile('*.txt','Select data file');
fid = fopen( strcat(PathName,FileName) ,'rt' );
% Read the file and store into matrix v
i = 0;
v = [0 0];
while feof(fid) == 0
    buffer = fscanf(fid, '%f', 2);
    buffer = buffer';
    if i == 0;
        v = buffer;
    else
        v = vertcat(v,buffer);
    end
    i = i + 1;
end
% Frequency vector
freq = v(:,1);
% Phase noise vector
pnoise = v(:,2);
figure
semilogx(freq,pnoise); grid on; axis([100 40^5 -160 -70]);
title('Simulated Phase Noise');
xlabel('Offset Frequency (Hz)'); ylabel('Phase Noise (dBc/Hz)');
return