filling an array with varivbles from a loop

Question

Luke Marchisin 2023-12-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2058814-filling-an-array-with-varivbles-from-a-loop

评论： Voss 2023-12-21

I need to fill 2 arrays with the values magnitude_db and phase_deg gained from a loop. however when i run the code it just fills the entire array with the last value. any help would be greatly appreciated.

A=.1;
omega=logspace(.1,10);
t = 0:0.01:500;
u=sin(A*t); 
y = eval_system(u,t); 
Unrecognized function or variable 'eval_system'.
phaseArray=[1,50];
for i=1:50
    f=omega(i);
    [magnitude_dB, phase_deg] = compute_mag_phase(t,u,y,f);
    magArray(1,i)=magnitude_dB;
    phaseArray(1,i)=phase_deg;
end

3 个评论
显示 1更早的评论隐藏 1更早的评论

Matt J 2023-12-10

The problem doesn't come from any of the code you've shown us. It comes from whatever eval_system and compute_mag_phase are doing.

Voss 2023-12-21

在 MATLAB Online 中打开

@Luke Marchisin: Note that logspace(a,b) generates values between 10^a and 10^b, so logspace(0.1,10) gives you values between 10^0.1 and 10^10. Perhaps you meant to say logspace(-1,1), which would give you values between 10^-1=0.1 and 10^1=10.

format long g
logspace(0.1,10,8).' % generating only 8 values, for brevity of display
ans = 8×1
1.0e+00 *

          1.25892541179417
          32.6802758941013
          848.342898244073
          22022.0194998737
          571666.650191362
          14839817.8896756
          385224842.003675
               10000000000
logspace(-1,1,8).'
ans = 8×1
                       0.1
         0.193069772888325
         0.372759372031494
         0.719685673001152
          1.38949549437314
          2.68269579527973
          5.17947467923121
                        10

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

SAI SRUJAN 2023-12-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2058814-filling-an-array-with-varivbles-from-a-loop#answer_1375742

在 MATLAB Online 中打开

Hi Luke,

I understand that you are facing an issue while trying to fill two arrays 'magArray' and 'phaseArray' with the magnitude in decibels and phase in degrees, respectively, for each frequency in the 'omega' array. You are using a function 'compute_mag_phase' to calculate the magnitude and phase for each frequency.

Note that 'phaseArray=[1,50]' generates a vector with dimensions 1 x 2, where the initial element is 1 and the subsequent element is 50. This does not reshape 'phaseArray' into an array with dimensions 1 x 50.

The error message "Unrecognized function or variable 'eval_system' " indicates that the function 'eval_system' is not defined in your MATLAB path or current workspace. You need to define this function or ensure it is added to the path.

In the code snippet you provided, observe the following line:

[magnitude_dB, phase_deg] = compute_mag_phase(t,u,y,f);

It is evident that 'f' is the sole variable that varies with each iteration. Therefore, it is crucial to verify that the function 'compute_mag_phase' is properly designed to yield distinct values corresponding to the different 'f' values, as expected.

Here is the corrected version of your code with proper initialization of the arrays and a placeholders for the 'eval_system' and 'compute_mag_phase' functions, which you will need to define:

A = 0.1;
omega = logspace(0.1, 10, 50);
t = 0:0.01:500;
u = sin(A * t);
y = eval_system(u, t); % Define 'eval_system' function
% Initialize arrays to hold 50 elements each
magArray = zeros(1, 50);
phaseArray = zeros(1, 50);
for i = 1:50
    f = omega(i);
    [magnitude_dB, phase_deg] = compute_mag_phase(t, u, y, f); % Define 'compute_mag_phase' function
    magArray(1,i) = magnitude_dB; % Store magnitude in dB
    phaseArray(1,i) = phase_deg; % Store phase in degrees
end