How to find both of the local minimums in this plot ?

Hi All

just having the vectors of the axes , how can I find the minimums ?

[dpb]

What does "just having the vectors of the axes" mean, precisely? If you don't have the y-axis data values that plotted the curve, you have nothing. Of course, if you do have the figure by having been sent it as a .fig file say, but not the data that drew it, you can obtain such by finding the handle for the line on the axes and querying it for the '[x|y]data' properties.

[farzad]

I have both the x and y data

Answer 1

[Image Analyst]

If you have the Signal Processing Toolbox, invert your data and call findpeaks().

y = max(y) - y;
[peaks, indexes] = findpeaks(y);

[farzad]

thank you

I attached my x and y , I think it didn't work correctly

[dpb]

This just translates the waveform, you want to negate it instead...

[peaks, indexes] = findpeaks(-y);

[Image Analyst]

farzad, I don't know what you tried since you didn't attach your code. So I made a full demo:

s = load('y.mat')
y = s.weight;
s = load('x.mat')
x = s.D11;

% Plot original data.
subplot(1,2,1);
plot(x, y, 'b-', 'LineWidth', 3)
grid on;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);

% Flip the data.
yFlipped = max(y) - y;
% Plot flipped data.
subplot(1,2,2);
plot(x, yFlipped, 'b-', 'LineWidth', 3)
grid on;

[peaks, indexes] = findpeaks(yFlipped)
xPeaks = x(indexes)

% Indicate the peaks on the flipped graph
hold on;
plot(xPeaks, peaks, 'r*', 'LineWidth', 3, 'MarkerSize', 15);

% Go back to the unflipped plot and indicate them.
subplot(1,2,1);
hold on;
plot(xPeaks, y(indexes), 'r*', 'LineWidth', 3, 'MarkerSize', 15);

% Draw lines from lower axis to valleys
yl = ylim();
for k = 1 : length(peaks);
  line([xPeaks(k), xPeaks(k)], [yl(1), y(indexes(k))], ...
    'LineWidth', 3, 'Color', 'm');
end

dpb, it flips the data, not translates it. Though I agree, it could be done with -y instead of max(y)-y.

[farzad]

Thanks a lot !