Finding coordinates in a plot

I have to find halfwidth of a curve I have plotted for this I need to find half of maximum value in the plot and their corresponding coordinates.How do I find it?

[darova]

Where is the curve?

[Tanmay Singh]

Answer 1

[Star Strider]

I hope this is not homework!

x = linspace(-5000, 5000, 250);
y = [7.5; 1.9; 0.9] .* exp(-(0.001*[1; 0.85; 0.6] * x).^2);
[ymx,idx] = max(y,[],2);
hafmax = ymx/2;
for k = 1:numel(hafmax)
    idxrng1 = find(y(k,1:idx(k))<hafmax(k), 1, 'last');
    idxrng2 = find(y(k,idx(k):numel(x))<hafmax(k),1,'first')+idx(k);
    xm(k,1) = interp1(y(k,idxrng1+(-3:3)), x(idxrng1+(-3:3)), hafmax(k));
    xm(k,2) = interp1(y(k,idxrng2+(-3:3)), x(idxrng2+(-3:3)), hafmax(k));
end

format short g
xm

xm = 3×2

-832.87 832.87 -979.71 979.71 -1387.7 1387.7

format short

figure
plot(x, y)
hold on
for k = 1:numel(hafmax)
    plot([xm(k,1) xm(k,2)], [1 1]*hafmax(k), '-k', 'LineWidth',1.5)
end
hold off
grid
xlim([-1 1]*2000)

Make appropriate changes with respect to your data.

.

[Tanmay Singh]

Thankyou..!

[Star Strider]

As always, my pleasure!

.

Answer 2

[darova]

Use polyxpoly

x1 = 0:.1:pi;       % first curve
y1 = sin(x1);
x2 = [0 pi];        % straight line for findinf intersection
y2 = [1 1]*max(y1)/2;
[xc,yc] = polyxpoly(x1,y1,x2,y2);
plot(xc,yc,'.r')
line(x1,y1)
line(x2,y2)

[Tanmay Singh]

thanks alot..!