help with this code. I keep getting error message

when i execute the code below, i get the error message - Array indices must be positive integers or logical values.

n=30
t=0;    % initialisation
for t=1:1:n     %time intervals
    s(t)=sum(v(t-1));   %cumulative sum of the values before current value
    s(t)=sum(v(t))+s(t-1);  %cumulative sum of values up to current value
    g(t)=v(t) - min(v);    %current value minus minimum value in the matrix from first iteration to current iteration 
    if s(t) > 4
        disp(t)         %notify the time of change
     disp(v(t))             % if cumulative sum is greater than 4, display when change occurs
    end
    t=t+1;
end

note: v is a 1x30 vector.

Answer 1

[Adam Danz]

If you format your code using the {} button, people can help you more easily.

The first problem I see is the line below. On the first iteration, t = 1 so v(t-1) is v(0). As the error message indicates, indices must be positive integers or logicals. Here, 0 is neither and you're requesting the 0_th value of t which causes the error.

s(t)=sum(v(t-1));

Also, there's no sense in initializing t=0 prior to your for-loop where you redefine t as 1:1:n.

[Folakemi Omotoye]

i don't want to use cell array as it will complicate the code for me to handle

[Adam Danz]

Cell arrays have nothing to do with my answer. Did you understand what is causing the error?

[Folakemi Omotoye]

yes. i have removed it.what i wanted to write in the line is to add the sum of previous iteration and the sum of current iteration

[Adam Danz]

You'll need to edit your question and format your code for me to easily read your code. Use the {} button.

[Dennis]

If v is a vector/matrix v(t) will only return 1 value each iteration. sum(v(t)) will be the same as v(t) since you are summing up only 1 value. If you want to sum up all values up to t in a loop you can do it like this:

for t=1:30
s(t)=sum(v(1:t));  
end

[Folakemi Omotoye]

n=30 v= 1x300 vector

for t=1:1:n %time intervals

    s(t)=sum(v(t))+sum(v(1:t));  %cumulative sum up to current value

    g(t)=v(t) - min(v);    %current value minus minimum value up to current value

    if s(t) > 4
        disp(t)         %notify the time of change

     disp(v(t))             % if cumulative sum is greater than 4,note and display time of change

    end
    t=t+1;

    plot(t,v(t))

end after implementing your corrections, the error message is that index exceeds array bounds

[Adam Danz]

Cumulative sum to current value would be this:

s(t)= sum(v(1:t));

More importantly, remove this

t = t+1;

That's the purpose of the loop. You're looping through values of t already.

If that doesn't fix the error, please let us know what line is producing the error in your updated code.

[Folakemi Omotoye]

thanks i have removed that but i keep getting an error. this is the new code for t=1:1:n %time intervals

    s(t)=sum(v(t))+sum(v(1:t));  %cumulative sum up to current value

    g(t)=v(t) - min(v(1:t));    %current value minus minimum value up to current 
    if s(t) > 4
        disp(t)         %notify the time of change
     disp(v(t))             % if cumulative sum is greater than 4,note and display time of change
    end

    figure(1), subplot(2,1,1)
    plot(t,v(t))

    title('signal change plot')
    xlabel('time (ms)')
    ylabel('Amplitude (v)')
end

[Dennis]

minimum value up to current value would be:

min(v(1:t))

what are you trying to plot? your plot command probably is not doing what you want :)

[Adam Danz]

Folakemi, it will be easier to help you if you format your code properly so that all of your code is within the { } brackets. Also, when you have an error, tell us exactly what the error is and which line is causing the error.

[Folakemi Omotoye]

how do i use the curly brackets. I am new to matlab. i have written the code below within curly brackets, i don't if this is what you mean by using the curly bracket

{for t=1:1:n     %time intervals

    s(t)=sum(v(t))+sum(v(1:t));  %cumulative sum up to current value

    g(t)=v(t) - min(v(1:t));    %current value minus minimum value up to current value

    if s(t) > 4
        disp(t)         %notify the time of change

     disp(v(t))             % if cumulative sum is greater than 4,note and display time of change

    end

    plot(t,v(t))

    title('signal change plot')
    xlabel('time (ms)')
    ylabel('Amplitude (v)')
end}

i do not know which line is giving the error. matlab did not indicate the line. it one of the reasons why im confused. it just did not plot

[Folakemi Omotoye]

line {min(v(1:t)) } is to find the minimum in the vector up to the current value of t

[Dennis]

Thats why i asked what you want to plot. plot(t,v(t)) will only plot one point and you are overwriting every plot in each loop iteration. Try:

for t=1:1:n     %time intervals

      s(t)=sum(v(1:t));  %cumulative sum up to current value

      g(t)=v(t) - min(v(1:t));    %current value minus minimum value up to current value

      if s(t) > 4
          disp(t)         %notify the time of change

       disp(v(t))             % if cumulative sum is greater than 4,note and display time of change

      end
  end
      plot(1:t,v(1:t))

      title('signal change plot')
      xlabel('time (ms)')
      ylabel('Amplitude (v)')

[Adam Danz]

Folakemi, when you include code in these comments, use this button to format the code.

I can't help you without knowing exactly what error message you're getting. Please cut and paste the entire error message into the comments.

[Folakemi Omotoye]

it worked. Thank you so much and everyone's contributions.i really appreciate.