Plotting FRF with imaginary and real numbers

Hello, I have a file of all the FRF functions of an experiment, and it is computed in complex numbers + real part. I would like to know if it is possible to plot the graphic of it (resulting in the natural frequencies and stuff) only having this data?

it is like this:

-0.0915237963199616 + 0.00000000000000i -0.0666214004158974 - 0.0629538968205452i -0.0647708997130394 - 0.0962110981345177i 0.000384484999813139 - 0.189506992697716i 0.104717001318932 - 0.171706005930901i 0.145686000585556 - 0.117163002490997i 0.148408994078636 - 0.0817890018224716i 0.150115996599197 - 0.0637563988566399i 0.149434000253677 - 0.0457847006618977i 0.151601999998093 - 0.0343611985445023i 0.144703000783920 - 0.0156481992453337i 0.134606003761292 - 0.00748514989390969i 0.119563996791840 - 0.00314980000257492i and so on

Answer 1

[Star Strider]

‘I would like to know if it is possible to plot the graphic of it (resulting in the natural frequencies and stuff) only having this data?’

It is.

However you also need to have the associated frequency vector if you want to make any sense of it.

[Ana Bianco]

Makes sense! Thank you !

[Star Strider]

My pleasure!

For data you posted, and with the appropriate frequency vector (I created one here), this would work:

FRF = [ -0.0915237963199616 + 0.00000000000000i;	-0.0666214004158974 - 0.0629538968205452i;	-0.0647708997130394 - 0.0962110981345177i;	0.000384484999813139 - 0.189506992697716i;	0.104717001318932 - 0.171706005930901i;	0.145686000585556 - 0.117163002490997i;	0.148408994078636 - 0.0817890018224716i;	0.150115996599197 - 0.0637563988566399i;	0.149434000253677 - 0.0457847006618977i;	0.151601999998093 - 0.0343611985445023i;	0.144703000783920 - 0.0156481992453337i;	0.134606003761292 - 0.00748514989390969i;	0.119563996791840 - 0.00314980000257492i];
Fv = linspace(0, 10, numel(FRF));                           % Frequency Vector

figure
plot(Fv, abs(FRF))
grid
xlabel('Frequency')
ylabel('Amplitude')

Experiment to get the result you want.

[Ana Bianco]

It worked perfectly well, thank you!

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!

[Ana Bianco]

Another thing... the results I have were generated from 0 to 8000 hz, and the FRF's (imaginary and real part) were generated for each 0,625 hz, so we got here 12800. But instead of plotting a graphic for each 12800 point, i want to make the frequency sample for each 10 hz, "smoothing" the function. Is it possible? How can I write down this frequency vector?

[Star Strider]

I actually have no idea, because none of those numbers were in your original question.

Try this:

FRF = [ -0.0915237963199616 + 0.00000000000000i;	-0.0666214004158974 - 0.0629538968205452i;	-0.0647708997130394 - 0.0962110981345177i;	0.000384484999813139 - 0.189506992697716i;	0.104717001318932 - 0.171706005930901i;	0.145686000585556 - 0.117163002490997i;	0.148408994078636 - 0.0817890018224716i;	0.150115996599197 - 0.0637563988566399i;	0.149434000253677 - 0.0457847006618977i;	0.151601999998093 - 0.0343611985445023i;	0.144703000783920 - 0.0156481992453337i;	0.134606003761292 - 0.00748514989390969i;	0.119563996791840 - 0.00314980000257492i];
Fv = linspace(0, 1, numel(FRF))*8000;                       % Frequency Vector
figure
plot(Fv, abs(FRF))
grid
xlabel('Frequency')
ylabel('Amplitude')

Fvi = linspace(0, 1, max(Fv)/10)*max(Fv);                   % New Frequency Vector
FRFi = interp1(Fv, abs(FRF), Fvi, 'pchip');                 % Interpolate

figure
plot(Fvi, FRFi)
grid
xlabel('Frequency')
ylabel('Amplitude')

Experiment to get the result you want.

[Ana Bianco]

Sorry about it, but ok, I'll try it! Thanks!