how to pass values from a .txt file

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francesco baldi
francesco baldi 2022-1-3
评论： Star Strider 2022-1-4
Hi there,
I have the following problem: I exported the transfer function of a circuit as a .txt file from LTSpice to Matlab. The txt file contains a list of frequency, real part values and imaginary part values of my transfer function. Now, i need to use these values to calculate another parameter of my circuit, always in its real and imaginary parts, but i don't know how to do it.
Supposing that the transfer function is called H, i need to calculate real and immaginary part of the parameter G for all the frequencies in the .txt:
Re(G) = (100*(Re(H) - (Re(H))^2 - (Im(H))^2))/(1 + (Re(H))^2 - 2*Re(H) + (Im(H))^2)
Im(G) = (100*Im(H))/(1 + (Re(H))^2 - 2*Re(H) + (Im(H))^2)
i attached the .txt file of the transfer function H.

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采纳的回答

Star Strider
Star Strider 2022-1-3
Ran in:
Reading the file was another interesting challenge!
Try this —
T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/851740/RC_parallelo_A.txt', 'VariableNamingRule','preserve')
T1 = 301×2 table
Freq. V(n002)/V(n001) ______ ________________________________________________ 1000 {'4.99507006345180e-001,-1.56924754155065e-002'} 1023.3 {'4.99483796257063e-001,-1.60572539733348e-002'} 1047.1 {'4.99459494622917e-001,-1.64304760271490e-002'} 1071.5 {'4.99434050222423e-001,-1.68123344493718e-002'} 1096.5 {'4.99407409442751e-001,-1.72030263342230e-002'} 1122 {'4.99379516167860e-001,-1.76027530768304e-002'} 1148.2 {'4.99350311662788e-001,-1.80117204528228e-002'} 1174.9 {'4.99319734452691e-001,-1.84301386983247e-002'} 1202.3 {'4.99287720196435e-001,-1.88582225902587e-002'} 1230.3 {'4.99254201554475e-001,-1.92961915268536e-002'} 1258.9 {'4.99219108050801e-001,-1.97442696082487e-002'} 1288.2 {'4.99182365928685e-001,-2.02026857170701e-002'} 1318.3 {'4.99143897999976e-001,-2.06716735988481e-002'} 1349 {'4.99103623487659e-001,-2.11514719421283e-002'} 1380.4 {'4.99061457861407e-001,-2.16423244581193e-002'} 1412.5 {'4.99017312665835e-001,-2.21444799597034e-002'}
T12 = cell2mat(T1{:,2});
for k = 1:size(T12,1)
T1{:,2}{k,:} = str2num(strrep(T12(k,:), ',',' '));
end
Freq = T1.('Freq.');
V = cell2mat(T1{:,2});
ReV = V(:,1);
ImV = V(:,2);
H = ReV + 1j*ImV;
Re = @(H) real(H);
Im = @(H) imag(H);
ReG = (100*(Re(H) - (Re(H)).^2 - (Im(H)).^2))./(1 + (Re(H)).^2 - 2*Re(H) + (Im(H)).^2);
ImG = (100*Im(H))./(1 + (Re(H)).^2 - 2*Re(H) + (Im(H)).^2);
CxG = ReG + 1j*ImG;
figure
subplot(2,1,1)
semilogx(Freq, mag2db(abs(CxG)))
grid
ylabel('Magnitude (dB)')
subplot(2,1,2)
semilogx(Freq, rad2deg(angle(CxG)))
grid
xlabel('Frequency')
ylabel('Phase (°)')
sgtitle('Transfer Function Bode Plot of ‘G’')
.
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显示 11更早的评论
Walter Roberson
Walter Roberson 2022-1-4
Ran in:
filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/852285/RLCAcart.txt';
S = webread(filename);
data = cell2mat(textscan(S, '%f %f,%f', 'headerlines', 1));
format long g
data(1:5,:)
ans = 5×3
1.0e+00 * 1000 8.90096842969402e-05 0.00628442202450237 1023.29299228075 9.27357685256782e-05 0.00643087677904904 1047.1285480509 9.66376954297881e-05 0.00658074803514854 1071.51930523761 0.000100723775170423 0.00673411574036376 1096.47819614319 0.000105002711771054 0.00689106173072146
Star Strider
Star Strider 2022-1-4
I didn’t even consider webread since I very seldom do anything with MATLAB and web pages, so I have little experience with it. That’s certainly a work-around to avoid the problems with fopen.

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更多回答（1 个）

Walter Roberson
Walter Roberson 2022-1-3
Ran in:
filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/851740/RC_parallelo_A.txt';
S = webread(filename);
parts = regexp(S, '(?<freq>-?\d\S+)\s+(?<real>-?\d[^\s,]+),(?<imag>-?\d\S)', 'names');
freqs = str2double({parts.freq});
ReH = str2double({parts.real});
ImH = str2double({parts.imag});
ReG = (100*(ReH - (ReH).^2 - (ImH).^2))./(1 + (ReH).^2 - 2*ReH + (ImH).^2);
ImG = (100*ImH)./(1 + (ReH).^2 - 2*ReH + (ImH).^2);
G = complex(ReG, ImG);
[sReH, hIdx] = sort(ReH); sImH = ImH(hIdx);
plot(sReH, sImH); title('real H vs imag H')
[sReG, gIdx] = sort(ReG); sImG = ImG(gIdx);
plot(sReG, sImG); title('real G vs imag G')

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