Finding when spline interpolated data is equal to a number

Hello, how would you determine when spline interpolated data is equal to some number, e.g. 3?

Thanks!

Answer 1

[Stephen23]

X = [1,2,3];
Y = [1,2,4];
Yq = 3;
pp = spline(X,Y);
fh = @(xq)ppval(pp,xq)-Yq;
Xq = fzero(fh,[1,4])

Xq = 2.5616

plot(X,Y,'+',Xq,Yq,'*')