MATLAB Answers

get the x-value of a point on curve

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ahmed salah
ahmed salah on 20 Feb 2020
Commented: the cyclist on 20 Feb 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 Comments
ahmed salah
ahmed salah on 20 Feb 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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Accepted Answer

the cyclist
the cyclist on 20 Feb 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 Comments

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More Answers (1)

Sky Sartorius
Sky Sartorius on 20 Feb 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 Comments
the cyclist
the cyclist on 20 Feb 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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