plot in matlab with timer on x axis

Question

I have a Matlab code which plots the variable value against the loop iterations.

I have considered random values as variable value just for this example.

function varargout = myplot(varargin)

gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @myplot_OpeningFcn, ...
                   'gui_OutputFcn',  @myplot_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT


% --- Executes just before myplot is made visible.
function myplot_OpeningFcn(hObject, eventdata, handles, varargin)

handles.output = hObject;
% Update handles structure
guidata(hObject, handles);


function varargout = myplot_OutputFcn(hObject, eventdata, handles) 

varargout{1} = handles.output;


% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
axes(handles.axes1);
iif = 0;
i = 1;
y = 0;
while (i < 1000)
    yf = rand(1);
    y = [y, yf];
    iif = [i,iif];
    i = i + 1;
    plot(iif,y);
    pause(0.001);
end

How can I replace iif = [i,iif]; into a timer ?

All I want to have is data plotted against the time(in seconds) instead of data vs loop iterations. Anyone have any idea ? Thanks.

Answer 1

You can use tic and toc to keep track of the seconds that have elapsed. tic starts the counter and all successive calls to toc return the seconds that have elapsed since the last tic .

iif = 0;
i = 1;
y = 0;

hplot = plot(iif, y);
xlabel('Elapsed Time (s)')
ylabel('Value')

% Force a graphics refresh so that isn't counted in our elapsed time
drawnow

% Start the timer
tic

while (i < 1000)
    yf = rand(1);
    y = cat(2, y, yf);

    % Call toc to get the current elapsed time
    iif = cat(2, iif, toc);

    i = i + 1;

    set(hplot, 'xdata', iif, 'ydata', y);
    pause(0.001)
end

As a side note, you could also write your loop as a for loop and pre-allocate all of your variables which will improve performance.

nIterations = 1000;
iif = nan(nIterations, 1);
y = nan(nIterations, 1);

hplot = plot(iif, y);

tic

for k = 1:nIterations
    y(k) = rand(1);
    iif(k) = toc;

    set(hplot, 'XData', iif, 'YData', y)
    pause(0.001)
end