Alternative to ginput for finding curve intersections with unevenly spaced data in MATLAB

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Bo
Bo 2025-2-8
编辑： Star Strider 2025-2-9
Is there a better way to determine the intersection of two curves in MATLAB, other than using ginput, especially when the data points are unevenly spaced and do not include the exact intersection point? How can I handle cases where one of my datasets forms two angled lines joined together, rather than a smooth curve?

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采纳的回答

Matt J
Matt J 2025-2-8
编辑：Matt J 2025-2-8
Ran in:
Use fminbnd or fzero,
x=sort(rand(1,12)*5);
y1=[0,1,-1*x(3:end)+3+2*x(3)];
y2=2*x-3;
f=@(z) interp1(x,y1,z)-interp1(x,y2,z) ;
xmin=fzero(f,[min(x),max(x)]); ymin=interp1(x,y1,xmin); %intersection
h=plot(x,y1,'--gx', x,y2,'--b+',xmin,ymin,'ro');
h(3).MarkerFaceColor=h(3).Color; h(3).MarkerSize=8;
●

更多回答（2 个）

Alan Stevens
Alan Stevens 2025-2-8
Ran in:
Create a function using interp1 for use with fzero. For example:
yfn = @(X,Y,x) interp1(X,Y,x);
X = [1,2,3,7,8,9];
Y1 = X;
Y2 = 15-X.^1.5;
x0 = 6;
xp = fzero(@(x0)fn(x0,X,Y1,Y2,yfn),x0);
disp(xp)
4.5710
yp = yfn(X,Y1,xp);
plot(X,Y1,'-o',X,Y2,'-+',xp,yp,'ks'),grid
xlabel('x'), ylabel('y')
●
function Z = fn(x,X,Y1,Y2,yfn)
Z = yfn(X,Y1,x)-yfn(X,Y2,x);
end
Star Strider
Star Strider 2025-2-8
编辑：Star Strider 2025-2-9
Ran in:
Another approach —
x = [linspace(0, 2.4) linspace(5.2, 7, 8)].'*1E-3;
y1 = [x(x<=2.4E-3)*580/2.4E-3; 500*ones(size(x(x>2.5E-3)))];
y2 = x*580/2.4E-3 - 450;
idx = find(diff(sign(y2 - y1)))
idx = 100
idxrng = max(1,idx) : min(numel(x),idx+1)
idxrng = 1×2
100 101
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
y2(idxrng)-y1(idxrng)
ans = 2×1
-450.0000 306.6667
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
xi = interp1((y1(idxrng)-y2(idxrng)), x(idxrng), 0)
xi = 0.0041
yi = interp1(x, y1, xi)
yi = 532.4229
figure
plot(x, y1, '.-', DisplayName="y_1")
hold on
plot(x, y2, '.-', DisplayName="y_2")
plot(xi, yi, 'sr', DisplayName="Intersection")
hold off
grid
legend(Location='best')
●
This approach finds the approximate index of the two lines and then interpolates to find the intersection points of the lines.
EDIT — (9 Feb 2025 at 1:43)
Corrected code.
.

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