Index exceeds the number of array elements. Index must not exceed 1.

function cost = optimize_PID(k)

assignin('base', 'k', k);

sim('DABvoltagecontrol.slx');

ITAE = load('ITAE.mat');

num_samples = size(ITAE.ans , 1);

ITAE_value = ITAE.ans(1, num_samples);

cost = ITAE_value(num_samples);

end

while executing the code, error is showing : Index exceeds the number of array elements. Index must not exceed 1. the ITAE is loaded to .mat format

Answer 1

[Torsten]

num_samples = size(ITAE.ans , 1);
ITAE_value = ITAE.ans(1, num_samples);

num_samples is the number of rows of ITAE.ans, but you use it in setting ITAE_value as if it were the number of columns.

Maybe you mean

ITAE_value = ITAE.ans(num_samples,1);

?

[Deepti t]

Still the error shows.

Index exceeds the number of array elements. Index must not

exceed 1.

Error in optimize_PID (line 7)

cost = ITAE_value(num_samples);

[Torsten]

ITAE_value is a scalar - there is no element number num_samples of ITAE_value because there is only one.

Answer 2

[Sam Chak]

Hi @Deepti t

I would recommend calculating the ITAE (Integral of Time-weighted Absolute Error) within the Simulink model and connecting the output to the 'Outport' block. This approach is more straightforward. However, it appears that you are searching for a single parameter, k in the 3-gain PID controller, to minimize the ITAE. Here is a code snippet that may help you with that:

function cost = optimize_PID(k)
    assignin('base', 'k', k);
    [t, x, y] = sim('DABvoltagecontrol.slx');
    cost      = y(end, 1);  % number 1 Outport block
end

[Deepti t]

In this k variable i had assigned for propotional gain and integral gain as k=[0.15 50], in your code :[t, x, y] = sim('DABvoltagecontrol.slx'); i didnt get what this x, y variable stands for?

[Sam Chak]

The output argument [t, x, y] represents variable names for time logging, state vector logging, and output vector logging, respectively. I'm curious why you are loading the file 'ITAE.mat'. My guess is that your 'sim()' function sends some data to the Workspace using default variable names (which you didn't disclose). However, feel free to follow your instincts.

[Deepti t]

Initially the ITAE values i loaded to "to workspace" with out.ITAE. when i am trying to call the variable out.ITAE in the function, error is showing. that is why i changed to .mat. when i am givinig to out.ITAE after running the simulink model, i am able to get the values in the command window from out.ITAE. But I am not able to get the data when i am including in the function.

[Sam Chak]

Hi @Deepti t

I understand. So you mentioned that you have sent the data to the Workspace. Could you take some random stabilizing PID gains and plot the ITAE result? It would be helpful to see if the process is successful or not. I assume that your variable name for time logging is 'tout'. You can plot the data using the command: 'plot(out.tout, out.ITAE)', and remember to turn on the grid for better visualization.

plot(out.tout, out.ITAE), grid on

[Deepti t]

plotted the ITAE with respect to time.

[Sam Chak]

Hi @Deepti t

Thank you for your prompt update. I reviewed the graph, and there doesn't appear to be any issues with the logged data 'out.ITAE' (a vector), although it didn't converge. Please keep in mind that the optimizer only minimizes the final value of the graph, which is a scalar.

Give this 'function' a try and let me know if it works:

function cost = optimize_PID(k)
    assignin('base', 'k', k);
    tspan   = [0, 0.2];
    out     = sim('DABvoltagecontrol.slx', tspan);
    cost    = out.ITAE(end);
end

[Deepti t]

out.ITAE

timeseries

Common Properties:

Name: ''

Time: [328012x1 double]

TimeInfo: [1x1 tsdata.timemetadata]

Data: [328012x1 double]

DataInfo: [1x1 tsdata.datametadata]

No, still error is showing" unrecognised fileld ITAE", similarly i have saved the format in array, but when i am giving in command window: out.ITAE, its showing timeseries format

[Sam Chak]

Hi @Deepti t

I understand. It seems that my original approach in the initial answer would be more suitable, as it would eliminate the need for additional settings. In your case, you simply want to send the ITAE vector array to the Workspace.

However, if you prefer to stick with the To Workspace block, you can set the data format as 'Array'. By default, it is set to 'Time series', but not many non-programming people are familiar with how to use it in MATLAB.

[Deepti t]

I am able to get out.ITAE in the array format and also the cost variable showing the out.ITAE values, but the whole function is not working, " unrecognised field: ITAE"

[Sam Chak]

But your error says that out.ITAE is a time series data. Despite setting the To Workspace block to send data as 'Array', it seems that the logged data is still in the 'Time series' format. Am I missing something?

out.ITAE

timeseries

Common Properties:

Name: ''

Time: [328012x1 double]

TimeInfo: [1x1 tsdata.timemetadata]