How to calculate FWHM on the graph

Dear All,

I have graph attached.

Anyone can help me to calculate the FWHM based on my graph attached?

Answer 1

[Star Strider]

Try this —

LD1 = load('xstats.mat');
xstats = LD1.xstats

xstats = struct with fields:
       min: 0
       max: 24.3294
      mean: 12.1647
    median: 12.1647
      mode: 0
       std: 7.4434
     range: 24.3294

LD2 = load('ystats.mat');
ystats = LD2.ystats

ystats = struct with fields:
       min: 496
       max: 3189
      mean: 1.3102e+03
    median: 857
      mode: 498
       std: 933.9319
     range: 2693

F = openfig('graph.fig');

Lines = findobj(F, 'Type','Line');
x = Lines.XData;
y = Lines.YData;



wx = fwhm(x,y)

Pulse Polarity = Positive
Pulse is Impulse or Rectangular with 2 edges

wx = 8.0080

[wm,xr,hm] = myFWHM(x,y)

wm = 6.9718

xr = 1×2

9.0430 16.0148

hm = 1.3460e+03

[ymax,idx] = max(y);
ymin = min(y);

figure
plot(x, y)
hold on
plot(xr, [1 1]*hm+ymin, '.-r')
hold off
grid
text(x(idx), hm+ymin, sprintf('FWHM = %.3f',wm), 'Horiz','center', 'Vert','bottom')

% ylim([min(y) max(y)])

function [width,xr,hm] = myFWHM(x, y)
p1 = polyfit(x([1 end]), y([1 end]), 1);
y_dtrnd = y - polyval(p1,x);
[ymax,yidx] = max(y_dtrnd);
[ymin,xidx] = min(y_dtrnd);
idxrng = {1:yidx; yidx:numel(y)};
hm = (ymax-ymin)/2;
xr(1) = interp1(y_dtrnd(idxrng{1})-ymin, x(idxrng{1}), hm, 'linear');
xr(2) = interp1(y_dtrnd(idxrng{2})-ymin, x(idxrng{2}), hm, 'linear');
width = xr(2)-xr(1);
end

The .mat files do not appear to add any useful information. The ‘fwhm’ function does not appear to correct forr a non-zero baseline.

.

[mohd akmal masud]

tahnk you @Star Strider, I think the FWHM =6.972 is correct.

But what is the meaning of value below:

wx = 8.0080

wm = 6.9718

xr = 1×2

9.0430 16.0148

hm = 1.3460e+03

[Star Strider]

The ‘wx’ value is the width that the ‘fwhm’ function calculates. It calculates from zero, not from the function minimum.

For the others, ‘wm’ is the width (FWHM) my function calculates, ‘xr’ are the width points it returns (the difference between them is ‘xm’), and ‘hm’ is the half-maximum value my function returns. (I use them in the plot and the text arguments.) My function uses the funciton minnimum, rather than zero, to calculate all the necessary values. The title of your Question refers to ‘on the graph’ so I assume you want them all plotted. I presented all of the necessary information on the plot.

I still do not know what ‘xstats’ and ‘ystats’ refer to, however my earlier Answer calculated the widths with respect to ‘cx’ and ‘cy’ as well as the figure data.

.

Answer 2

[Andrei]

The findpeaks function in Signal Processing Toolbox can be used to determine the width (full width) of the detected peaks. By default, the peak widths (output w in the example below) are calculated at half prominence. You can also specify the reference height for peak width measurements, WidthReference name-value pair, as "halfprom" or "halfheight".

x = linspace(-5, 5, 101);
y = exp(-x.^2);


[pks,locs,w,p] = findpeaks(y,x)