get the x-value of a point on curve

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ahmed salah
ahmed salah el 20 de Feb. de 2020
Comentada: the cyclist el 20 de Feb. de 2020
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 comentarios
Jon
Jon el 20 de Feb. de 2020
Please post your code
ahmed salah
ahmed salah el 20 de Feb. de 2020
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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Respuesta aceptada

the cyclist
the cyclist el 20 de Feb. de 2020
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 comentarios
the cyclist
the cyclist el 20 de Feb. de 2020
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.
ahmed salah
ahmed salah el 20 de Feb. de 2020
Thank you

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Más respuestas (1)

Sky Sartorius
Sky Sartorius el 20 de Feb. de 2020
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 comentarios
ahmed salah
ahmed salah el 20 de Feb. de 2020
Thank you this worked for me
the cyclist
the cyclist el 20 de Feb. de 2020
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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