how to pass values from a .txt file

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.

Answer 1

[Star Strider]

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’')

.

[francesco baldi]

thank you, this is what i was looking for.

Once i have CxG = ReG + 1j*ImG, how can i calculate its modulus and phase to express it in polar coordinates instead of cartesian?

And what if i have to do the same thing with this other file i'm attaching? The difference between the two files is that the one i'm attaching here has frequency, dB and phase of the transfer function instead of frequency, real part and imag part, but the transfer function is exactly the same so i expect to obtain the same result of the code you just posted.

[Star Strider]

My pleasure!

I am not exactly certain what ‘modulus’ refers to in this context.

If it is the amplitude, then —

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
polarplot(angle(CxG), abs(CxG))                     % Angle In Radians, Absolute Magnitude (Not dB)

The polarplot function offers some options for customising the plot that polar does not. If the desired result is something else, it may be necessary to use the pol2cart function to convert the polar coordinates to Cartesian, and plot them as such, since not all functions work with polaraxes plots. (They will appear as polar plots, although plotted on Cartesian rectangular coordinates.)

.

[francesco baldi]

i'm sorry, that's not what i meant. "CxG = ReG + 1j*ImG" is a complex number expressed in cartesian coordinates(Re + jIm). I'd like to visualize it in polar coordinates, something like "abs(G)*exp(1j*angle(G))".

Other than this, can you tell me how to obtain the same result of your first answer with the file i'm attaching here? The previous code is not appropriate for this file , because in this file the transfer function was exported in polar coordinates, so in this file i have a list of frequencies, magnitude(dB) and phase(deg).

[Star Strider]

I’ll look at it in a minute.

I need to understand something. Do you want it as a polar plot, or as phasor (magnitude & phase) notation?

The phasor notation is easy —

Gphasor = [abs(CxG) angle(CxG)]

Then, multiplication of two phasors involves multiplying the first values (‘Gphasor(:,1)’) and adding the second values (‘Gphasor(:,2)’), with division being the reverse. The angle calculation uses the atan2 function, so it maps to all quadrants correctly.

Now, I’ll take a look at the file.

.

[Star Strider]

That was like one of the previous files, so I just copied the code over to here.

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/852005/RC_parallelo_A2.txt', 'VariableNamingRule','preserve')

T1 = 301×2 table
    Freq.                        V(n002)/V(n001)                    
    ______    ______________________________________________________

      1000    {'(-6.02488411418877e+000dB,-1.79940817416164e+000°)'}
    1023.3    {'(-6.02508591811268e+000dB,-1.84129325097736e+000°)'}
    1047.1    {'(-6.02529722271243e+000dB,-1.88415191829931e+000°)'}
    1071.5    {'(-6.02551847477256e+000dB,-1.92800670840101e+000°)'}
    1096.5    {'(-6.02575014204059e+000dB,-1.97288066801541e+000°)'}
      1122    {'(-6.02599271420608e+000dB,-2.01879736957869e+000°)'}
    1148.2    {'(-6.02624670392482e+000dB,-2.06578092268335e+000°)'}
    1174.9    {'(-6.02651264789045e+000dB,-2.11385598574197e+000°)'}
    1202.3    {'(-6.02679110795550e+000dB,-2.16304777786236e+000°)'}
    1230.3    {'(-6.02708267230413e+000dB,-2.21338209093502e+000°)'}
    1258.9    {'(-6.02738795667891e+000dB,-2.26488530193302e+000°)'}
    1288.2    {'(-6.02770760566403e+000dB,-2.31758438542470e+000°)'}
    1318.3    {'(-6.02804229402756e+000dB,-2.37150692629869e+000°)'}
      1349    {'(-6.02839272812519e+000dB,-2.42668113270082e+000°)'}
    1380.4    {'(-6.02875964736851e+000dB,-2.48313584918177e+000°)'}
    1412.5    {'(-6.02914382576040e+000dB,-2.54090057005413e+000°)'}

V2c = cellfun(@(x)sscanf(x, '(%fdB,%f°'), T1.('V(n002)/V(n001)'), 'Unif',0);
V2m = cell2mat(V2c')';
T2 = table('Size',[size(T1.('Freq.'),1) 3],'VariableTypes',{'double','double','double'}, 'VariableNames',{'FreqHz','MagndB','PhasDg'});
T2.FreqHz = T1.('Freq.');
T2.MagndB = V2m(:,1);
T2.PhasDg = V2m(:,2)

T2 = 301×3 table
    FreqHz    MagndB     PhasDg 
    ______    _______    _______

      1000    -6.0249    -1.7994
    1023.3    -6.0251    -1.8413
    1047.1    -6.0253    -1.8842
    1071.5    -6.0255     -1.928
    1096.5    -6.0258    -1.9729
      1122     -6.026    -2.0188
    1148.2    -6.0262    -2.0658
    1174.9    -6.0265    -2.1139
    1202.3    -6.0268     -2.163
    1230.3    -6.0271    -2.2134
    1258.9    -6.0274    -2.2649
    1288.2    -6.0277    -2.3176
    1318.3     -6.028    -2.3715
      1349    -6.0284    -2.4267
    1380.4    -6.0288    -2.4831
    1412.5    -6.0291    -2.5409

MagnAbs = db2mag(T2.MagndB)                         % Absolute Magnitude (Not dB)

MagnAbs = 301×1

0.4998 0.4997 0.4997 0.4997 0.4997 0.4997 0.4997 0.4997 0.4996 0.4996

PhasRd = deg2rad(T2.PhasDg)                         % Pahse In Radians

PhasRd = 301×1

-0.0314 -0.0321 -0.0329 -0.0337 -0.0344 -0.0352 -0.0361 -0.0369 -0.0378 -0.0386

H = MagnAbs .* exp(1j*PhasRd)

H = 
   0.4995 - 0.0157i
   0.4995 - 0.0161i
   0.4995 - 0.0164i
   0.4994 - 0.0168i
   0.4994 - 0.0172i
   0.4994 - 0.0176i
   0.4994 - 0.0180i
   0.4993 - 0.0184i
   0.4993 - 0.0189i
   0.4993 - 0.0193i
   0.4992 - 0.0197i
   0.4992 - 0.0202i
   0.4991 - 0.0207i
   0.4991 - 0.0212i
   0.4991 - 0.0216i
   0.4990 - 0.0221i
   0.4990 - 0.0227i
   0.4989 - 0.0232i
   0.4989 - 0.0237i
   0.4988 - 0.0243i
   0.4988 - 0.0248i
   0.4987 - 0.0254i
   0.4986 - 0.0260i
   0.4986 - 0.0266i
   0.4985 - 0.0272i
   0.4984 - 0.0278i
   0.4984 - 0.0285i
   0.4983 - 0.0291i
   0.4982 - 0.0298i
   0.4981 - 0.0305i
   0.4980 - 0.0312i
   0.4980 - 0.0319i
   0.4979 - 0.0327i
   0.4978 - 0.0334i
   0.4976 - 0.0342i
   0.4975 - 0.0350i
   0.4974 - 0.0358i
   0.4973 - 0.0366i
   0.4972 - 0.0375i
   0.4970 - 0.0383i
   0.4969 - 0.0392i
   0.4968 - 0.0401i
   0.4966 - 0.0410i
   0.4965 - 0.0420i
   0.4963 - 0.0429i
   0.4961 - 0.0439i
   0.4959 - 0.0449i
   0.4957 - 0.0460i
   0.4955 - 0.0470i
   0.4953 - 0.0481i
   0.4951 - 0.0492i
   0.4949 - 0.0503i
   0.4946 - 0.0515i
   0.4944 - 0.0526i
   0.4941 - 0.0538i
   0.4939 - 0.0550i
   0.4936 - 0.0563i
   0.4933 - 0.0576i
   0.4930 - 0.0589i
   0.4926 - 0.0602i
   0.4923 - 0.0616i
   0.4919 - 0.0630i
   0.4916 - 0.0644i
   0.4912 - 0.0658i
   0.4908 - 0.0673i
   0.4903 - 0.0688i
   0.4899 - 0.0703i
   0.4894 - 0.0719i
   0.4889 - 0.0735i
   0.4884 - 0.0752i
   0.4879 - 0.0768i
   0.4873 - 0.0785i
   0.4868 - 0.0803i
   0.4862 - 0.0820i
   0.4855 - 0.0838i
   0.4849 - 0.0857i
   0.4842 - 0.0875i
   0.4835 - 0.0894i
   0.4827 - 0.0914i
   0.4819 - 0.0934i
   0.4811 - 0.0954i
   0.4802 - 0.0974i
   0.4793 - 0.0995i
   0.4784 - 0.1016i
   0.4774 - 0.1038i
   0.4764 - 0.1060i
   0.4754 - 0.1082i
   0.4743 - 0.1105i
   0.4731 - 0.1128i
   0.4719 - 0.1151i
   0.4707 - 0.1175i
   0.4694 - 0.1199i
   0.4680 - 0.1223i
   0.4666 - 0.1248i
   0.4652 - 0.1273i
   0.4637 - 0.1298i
   0.4621 - 0.1324i
   0.4604 - 0.1350i
   0.4587 - 0.1376i
   0.4569 - 0.1403i
   0.4551 - 0.1430i
   0.4532 - 0.1457i
   0.4512 - 0.1484i
   0.4491 - 0.1512i
   0.4470 - 0.1540i
   0.4447 - 0.1568i
   0.4424 - 0.1596i
   0.4400 - 0.1624i
   0.4376 - 0.1653i
   0.4350 - 0.1681i
   0.4324 - 0.1710i
   0.4296 - 0.1739i
   0.4268 - 0.1768i
   0.4239 - 0.1796i
   0.4209 - 0.1825i
   0.4177 - 0.1854i
   0.4145 - 0.1882i
   0.4112 - 0.1911i
   0.4078 - 0.1939i
   0.4043 - 0.1967i
   0.4007 - 0.1995i
   0.3970 - 0.2022i
   0.3931 - 0.2050i
   0.3892 - 0.2077i
   0.3852 - 0.2103i
   0.3811 - 0.2129i
   0.3768 - 0.2154i
   0.3725 - 0.2179i
   0.3681 - 0.2203i
   0.3636 - 0.2227i
   0.3590 - 0.2250i
   0.3542 - 0.2272i
   0.3494 - 0.2294i
   0.3446 - 0.2314i
   0.3396 - 0.2334i
   0.3345 - 0.2353i
   0.3294 - 0.2371i
   0.3242 - 0.2387i
   0.3189 - 0.2403i
   0.3135 - 0.2418i
   0.3081 - 0.2431i
   0.3026 - 0.2444i
   0.2971 - 0.2455i
   0.2915 - 0.2465i
   0.2859 - 0.2474i
   0.2803 - 0.2482i
   0.2746 - 0.2488i
   0.2689 - 0.2493i
   0.2631 - 0.2497i
   0.2574 - 0.2499i
   0.2516 - 0.2500i
   0.2459 - 0.2500i
   0.2401 - 0.2498i
   0.2344 - 0.2495i
   0.2287 - 0.2491i
   0.2230 - 0.2485i
   0.2173 - 0.2479i
   0.2117 - 0.2470i
   0.2061 - 0.2461i
   0.2005 - 0.2450i
   0.1950 - 0.2439i
   0.1895 - 0.2426i
   0.1842 - 0.2412i
   0.1788 - 0.2397i
   0.1736 - 0.2380i
   0.1684 - 0.2363i
   0.1633 - 0.2345i
   0.1583 - 0.2326i
   0.1533 - 0.2306i
   0.1485 - 0.2285i
   0.1437 - 0.2263i
   0.1390 - 0.2240i
   0.1345 - 0.2217i
   0.1300 - 0.2193i
   0.1256 - 0.2169i
   0.1213 - 0.2143i
   0.1171 - 0.2118i
   0.1131 - 0.2092i
   0.1091 - 0.2065i
   0.1052 - 0.2038i
   0.1014 - 0.2011i
   0.0978 - 0.1983i
   0.0942 - 0.1955i
   0.0907 - 0.1927i
   0.0874 - 0.1899i
   0.0841 - 0.1870i
   0.0809 - 0.1841i
   0.0778 - 0.1813i
   0.0749 - 0.1784i
   0.0720 - 0.1755i
   0.0692 - 0.1726i
   0.0665 - 0.1698i
   0.0639 - 0.1669i
   0.0614 - 0.1640i
   0.0589 - 0.1612i
   0.0566 - 0.1584i
   0.0543 - 0.1556i
   0.0521 - 0.1528i
   0.0500 - 0.1500i
   0.0480 - 0.1472i
   0.0460 - 0.1445i
   0.0441 - 0.1418i
   0.0423 - 0.1391i
   0.0405 - 0.1365i
   0.0389 - 0.1339i
   0.0372 - 0.1313i
   0.0357 - 0.1287i
   0.0342 - 0.1262i
   0.0328 - 0.1237i
   0.0314 - 0.1212i
   0.0300 - 0.1188i
   0.0288 - 0.1164i
   0.0275 - 0.1141i
   0.0264 - 0.1118i
   0.0252 - 0.1095i
   0.0242 - 0.1072i
   0.0231 - 0.1050i
   0.0221 - 0.1028i
   0.0212 - 0.1007i
   0.0203 - 0.0986i
   0.0194 - 0.0965i
   0.0185 - 0.0945i
   0.0177 - 0.0925i
   0.0170 - 0.0905i
   0.0162 - 0.0886i
   0.0155 - 0.0867i
   0.0148 - 0.0849i
   0.0142 - 0.0830i
   0.0136 - 0.0813i
   0.0130 - 0.0795i
   0.0124 - 0.0778i
   0.0119 - 0.0761i
   0.0113 - 0.0744i
   0.0108 - 0.0728i
   0.0104 - 0.0712i
   0.0099 - 0.0697i
   0.0095 - 0.0682i
   0.0091 - 0.0667i
   0.0087 - 0.0652i
   0.0083 - 0.0638i
   0.0079 - 0.0624i
   0.0076 - 0.0610i
   0.0072 - 0.0596i
   0.0069 - 0.0583i
   0.0066 - 0.0570i
   0.0063 - 0.0558i
   0.0060 - 0.0545i
   0.0057 - 0.0533i
   0.0055 - 0.0521i
   0.0052 - 0.0510i
   0.0050 - 0.0498i
   0.0048 - 0.0487i
   0.0046 - 0.0476i
   0.0044 - 0.0466i
   0.0042 - 0.0455i
   0.0040 - 0.0445i
   0.0038 - 0.0435i
   0.0036 - 0.0425i
   0.0035 - 0.0416i
   0.0033 - 0.0406i
   0.0032 - 0.0397i
   0.0030 - 0.0388i
   0.0029 - 0.0380i
   0.0028 - 0.0371i
   0.0026 - 0.0363i
   0.0025 - 0.0355i
   0.0024 - 0.0347i
   0.0023 - 0.0339i
   0.0022 - 0.0331i
   0.0021 - 0.0324i
   0.0020 - 0.0316i
   0.0019 - 0.0309i
   0.0018 - 0.0302i
   0.0018 - 0.0295i
   0.0017 - 0.0289i
   0.0016 - 0.0282i
   0.0015 - 0.0276i
   0.0015 - 0.0269i
   0.0014 - 0.0263i
   0.0013 - 0.0257i
   0.0013 - 0.0252i
   0.0012 - 0.0246i
   0.0012 - 0.0240i
   0.0011 - 0.0235i
   0.0011 - 0.0230i
   0.0010 - 0.0224i
   0.0010 - 0.0219i
   0.0009 - 0.0214i
   0.0009 - 0.0209i
   0.0008 - 0.0205i
   0.0008 - 0.0200i
   0.0008 - 0.0196i
   0.0007 - 0.0191i
   0.0007 - 0.0187i
   0.0007 - 0.0182i
   0.0006 - 0.0178i
   0.0006 - 0.0174i
   0.0006 - 0.0170i
   0.0006 - 0.0166i
   0.0005 - 0.0163i
   0.0005 - 0.0159i

% 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;
Gphasor = [abs(CxG) angle(CxG)]

Gphasor = 301×2

99.8032 -0.0627 99.7939 -0.0642 99.7843 -0.0657 99.7741 -0.0672 99.7635 -0.0688 99.7524 -0.0704 99.7408 -0.0720 99.7286 -0.0737 99.7159 -0.0754 99.7026 -0.0771

Is this the desired result? If not, what changes need to be made to the code?

.

[francesco baldi]

this is exactly what i meant, thank you.

[Star Strider]

As always, my pleasure!

.

[francesco baldi]

i tried this code with multiple transfer functions from different circuits and it works well, but i found one transfer function that's giving some problems. If i run the first code you wrote as an answer, i get this error:

Error using cat

Dimensions of arrays being concatenated are not consistent.

Error in cell2mat (line 83)

m{n} = cat(1,c{:,n});

it's pretty strange, since this transfer function has the same form (except for the values obviously) of others i tested with this code. Can you help me to fix this? I'm attaching here the .txt file that's creating problems.

[Star Strider]

These are becoming more difficult to parse, and my code to parse them less efficient.

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/852285/RLCAcart.txt', 'VariableNamingRule','preserve')

T1 = 301×2 table
    Freq.                     V(n002)/V(n001)                
    ______    _______________________________________________

      1000    {'8.90096842969402e-005,6.28442202450237e-003'}
    1023.3    {'9.27357685256782e-005,6.43087677904904e-003'}
    1047.1    {'9.66376954297881e-005,6.58074803514854e-003'}
    1071.5    {'1.00723775170423e-004,6.73411574036376e-003'}
    1096.5    {'1.05002711771054e-004,6.89106173072146e-003'}
      1122    {'1.09483621893805e-004,7.05166977657693e-003'}
    1148.2    {'1.14176054521385e-004,7.21602562968114e-003'}
    1174.9    {'1.19090011589333e-004,7.38421707148807e-003'}
    1202.3    {'1.24235969615539e-004,7.55633396274125e-003'}
    1230.3    {'1.29624902376463e-004,7.73246829438033e-003'}
    1258.9    {'1.35268304682028e-004,7.91271423981034e-003'}
    1288.2    {'1.41178217303880e-004,8.09716820857788e-003'}
    1318.3    {'1.47367253114530e-004,8.28592890150063e-003'}
      1349    {'1.53848624497986e-004,8.47909736729854e-003'}
    1380.4    {'1.60636172095583e-004,8.67677706077717e-003'}
    1412.5    {'1.67744394954195e-004,8.87907390261604e-003'}

for k = 1:size(T1,1)
    T1{:,2}{k,:} = str2num(strrep(cell2mat(T1{:,2}(k,:)), ',',' '));
end

ReIm = cell2mat(T1{:,2});

T2 = table('Size',[size(T1,1),3],'VariableTypes',{'double','double','double'}, 'VariableNames',{'Freq','Re','Im'});
T2.Freq = T1.('Freq.');
T2.Re = ReIm(:,1);
T2.Im = ReIm(:,2)

T2 = 301×3 table
     Freq         Re           Im    
    ______    __________    _________

      1000     8.901e-05    0.0062844
    1023.3    9.2736e-05    0.0064309
    1047.1    9.6638e-05    0.0065807
    1071.5    0.00010072    0.0067341
    1096.5      0.000105    0.0068911
      1122    0.00010948    0.0070517
    1148.2    0.00011418     0.007216
    1174.9    0.00011909    0.0073842
    1202.3    0.00012424    0.0075563
    1230.3    0.00012962    0.0077325
    1258.9    0.00013527    0.0079127
    1288.2    0.00014118    0.0080972
    1318.3    0.00014737    0.0082859
      1349    0.00015385    0.0084791
    1380.4    0.00016064    0.0086768
    1412.5    0.00016774    0.0088791

Freq = T2.Freq;
ReV = T2.Re;
ImV = T2.Im;
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)')
ylim([min(ylim) 45])
subplot(2,1,2)
semilogx(Freq, rad2deg(angle(CxG)))
grid
xlabel('Frequency')
ylabel('Phase (°)')
sgtitle('Transfer Function Bode Plot of ‘G’')

.

[francesco baldi]

Thank you, but what's the reason why this txt file gave problems? The txt file is always a list of 301 elements, I can't see any difference with the first txt I attached in my original question.

[Star Strider]

I don’t know. Since I was wondering too, I listed the entire file and didn’t see anything out of the ordinary, although I may have missed something. The code in the loop was able to parse the individual lines without problems. In any event, this now offers a new method of reading these files (added to that ‘library’ of methods), if another one has the same problems.

(I wish the detectImportOptions function was more straightforward and easier to use, since it might help with these. I don’t use it often enough to have any specific expertise with it. Once I get the files read, I may experiment with textscan on individual variables. It doesn’t work here to read the files, since fopen won’t open them. I’ll keep that in mind for next time.)

[Walter Roberson]

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]

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.

Answer 2

[Walter Roberson]

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')