How can i write this in matlab please

this is the whole code

    n=30;               
    [v]=linspace(3,20,n);
    %CUSUM Algorithm
    h=4;              %threshold
    t=2;
    for t=2:numel(v)         %start time
      s(t)=sum(v(t-1)+v(t));           %cumulative sum up to current value
      g(t)=max( s(2:t));            %maximum value
      if g(t) > h               %if output is greater than the specified threshold
        detect_tim=t(g(t)>h);                 %store the detection time
        disp(['The detection time= ', num2str(detect_tim),''])        %display the detection time
        %estimate the change time

%%%i need help here please.(please refer to attached pic for analogy-signal.jpg) from the attached figure, i want to specify the time when the signal started increasing from zero (point 1000).the threshold is known (red line in the pic) but the assumption should be that the value zero is unknown (i.e the value zero should be the cumulative sum in previous lines of code).i want to specify the time the signal significantly started increasing from the cumulative sum up till the threshold

        change_time=t(max(s(2:t))) ;       %the time following the current minimum of
        %the cumulative sum
        disp(['The change time estimate= ', num2str(change_time),''])          %display value of change
        % stop and reset algorithm
        continue               %to re-start algorithm
      end
    end

%Here, my xlim line doesnt get to the end of the length of the x-axis.it always stops at 1. i used auto because i don't know the last value of the x-axis. i want the horizontal line xl to extend till the end of the x-axis (signal plotpt1.jpg)

    xL = get(gca,'XLim');           %plot threshold line on same axis
    figure(1), subplot(2,1,1)
    line(xL,[4 4],'Color','r');   %horizontal line through the  threshold value
    hold on
    plot(2:t,v(2:t),'*b')           %the time vector plot
    title('signal change plot')
    xlabel('time (ms)')
    ylabel('Amplitude (v)')