get the x-value of a point on curve

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ahmed salah
ahmed salah 2020-2-20
评论： the cyclist 2020-2-20
I draw a curve between two vector of points, not a function, how can I get the x-value of a certain y-value of the curve?
  2 个评论
ahmed salah
ahmed salah 2020-2-20
here is the curve
x=[0,0.250000000000000,0.500000000000000,0.750000000000000,1,1.25000000000000,1.50000000000000,1.75000000000000,2,2.25000000000000,2.50000000000000,2.75000000000000,3,3.25000000000000,3.50000000000000,3.75000000000000,4,4.25000000000000,4.50000000000000,4.75000000000000,5,5.25000000000000,5.50000000000000,5.75000000000000,6,6.25000000000000,6.50000000000000,6.75000000000000,7,7.25000000000000,7.50000000000000,7.75000000000000,8,8.25000000000000,8.50000000000000,8.75000000000000,9,9.25000000000000,9.50000000000000,9.75000000000000,10,10.2500000000000,10.5000000000000,10.7500000000000,11,11.2500000000000,11.5000000000000,11.7500000000000,12,12.2500000000000,12.5000000000000,12.7500000000000,13,13.2500000000000,13.5000000000000,13.7500000000000,14,14.2500000000000,14.5000000000000,14.7500000000000,15,15.2500000000000,15.5000000000000,15.7500000000000,16,16.2500000000000,16.5000000000000,16.7500000000000,17,17.2500000000000,17.5000000000000,17.7500000000000,18,18.2500000000000,18.5000000000000,18.7500000000000,19,19.2500000000000,19.5000000000000,19.7500000000000,20,20.2500000000000,20.5000000000000,20.7500000000000,21,21.2500000000000,21.5000000000000,21.7500000000000,22,22.2500000000000,22.5000000000000,22.7500000000000,23,23.2500000000000,23.5000000000000,23.7500000000000,24,24.2500000000000,24.5000000000000,24.7500000000000,25,25.2500000000000,25.5000000000000,25.7500000000000,26,26.2500000000000,26.5000000000000,26.7500000000000,27,27.2500000000000,27.5000000000000,27.7500000000000,28,28.2500000000000,28.5000000000000,28.7500000000000,29,29.2500000000000,29.5000000000000,29.7500000000000,30,30.2500000000000,30.5000000000000,30.7500000000000,31,31.2500000000000,31.5000000000000,31.7500000000000,32,32.2500000000000,32.5000000000000,32.7500000000000,33,33.2500000000000,33.5000000000000,33.7500000000000,34,34.2500000000000,34.5000000000000,34.7500000000000,35,35.2500000000000,35.5000000000000,35.7500000000000,36,36.2500000000000,36.5000000000000,36.7500000000000,37,37.2500000000000,37.5000000000000,37.7500000000000,38,38.2500000000000,38.5000000000000,38.7500000000000,39,39.2500000000000,39.5000000000000,39.7500000000000,40,40.2500000000000,40.5000000000000,40.7500000000000,41,41.2500000000000,41.5000000000000,41.7500000000000,42,42.2500000000000,42.5000000000000,42.7500000000000,43,43.2500000000000,43.5000000000000,43.7500000000000,44,44.2500000000000,44.5000000000000,44.7500000000000,45,45.2500000000000,45.5000000000000,45.7500000000000,46,46.2500000000000,46.5000000000000,46.7500000000000,47,47.2500000000000,47.5000000000000,47.7500000000000,48,48.2500000000000,48.5000000000000,48.7500000000000,49,49.2500000000000,49.5000000000000,49.7500000000000,50,50.2500000000000,50.5000000000000,50.7500000000000,51,51.2500000000000,51.5000000000000,51.7500000000000,52,52.2500000000000,52.5000000000000,52.7500000000000,53,53.2500000000000,53.5000000000000,53.7500000000000,54,54.2500000000000,54.5000000000000,54.7500000000000,55,55.2500000000000,55.5000000000000,55.7500000000000,56,56.2500000000000,56.5000000000000,56.7500000000000,57,57.2500000000000,57.5000000000000,57.7500000000000,58,58.2500000000000,58.5000000000000,58.7500000000000,59,59.2500000000000,59.5000000000000,59.7500000000000,60,60.2500000000000,60.5000000000000,60.7500000000000,61,61.2500000000000,61.5000000000000,61.7500000000000,62,62.2500000000000,62.5000000000000,62.7500000000000,63,63.2500000000000,63.5000000000000,63.7500000000000,64,64.2500000000000,64.5000000000000,64.7500000000000,65,65.2500000000000,65.5000000000000,65.7500000000000,66,66.2500000000000,66.5000000000000,66.7500000000000,67,67.2500000000000,67.5000000000000,67.7500000000000,68,68.2500000000000,68.5000000000000,68.7500000000000,69,69.2500000000000,69.5000000000000,69.7500000000000,70,70.2500000000000,70.5000000000000,70.7500000000000,71,71.2500000000000,71.5000000000000,71.7500000000000,72,72.2500000000000,72.5000000000000,72.7500000000000,73,73.2500000000000,73.5000000000000,73.7500000000000,74,74.2500000000000,74.5000000000000,74.7500000000000,75,75.2500000000000,75.5000000000000,75.7500000000000,76,76.2500000000000,76.5000000000000,76.7500000000000,77,77.2500000000000,77.5000000000000,77.7500000000000,78,78.2500000000000,78.5000000000000,78.7500000000000,79,79.2500000000000,79.5000000000000,79.7500000000000,80];
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plot(x,y)

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采纳的回答

the cyclist
the cyclist 2020-2-20
When you say "get", do you mean from the vectors, or only from the curve?
If you mean from the data, you can do, for example
x(y==0.25)
(You might need to be careful if y is not exactly 0.25, due to floating point precision.)
  2 个评论
the cyclist
the cyclist 2020-2-20
My solution assumes the y value you are looking for is in the original vector. Sky Sartorius's solution is preferred if the y value is not in the original vector, but you want to interpolate.

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更多回答（1 个）

Sky Sartorius
Sky Sartorius 2020-2-20
This is a table lookup / interpolation problem. For your data, you'll first have to make sure there aren't any repeated y values.
yQuery = -2.6e8; % Example query point.
[Y,ind] = unique(y,'stable')
X = x(ind);
x = interp1(Y,X,yQuery)
  2 个评论
the cyclist
the cyclist 2020-2-20
The best way to thank a contributor is to upvote and/or accept their answer. This rewards them with reputation points, and also directs future users to solutions.

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