I have the Y co-ordinate to a very complex graph. How do I extract and plot the corresponding X coordinates?

22 次查看（过去 30 天）
Samar Kenkre
Samar Kenkre 2015-5-21
评论： Walter Roberson 2015-5-21
I can't generate the function of the graph because its too complex. I've plotted the graph using input data points. I have particular random values on the Y-axis and I need the corresponding X values. the find() function doesn't work because I think it only returns integral indices (Mine won't be an integral index).
  2 个评论
Image Analyst
Image Analyst 2015-5-21
How did you plot it with only the Y data? If you don't have any x values, then of course it will just use the index as the x values. If you don't have the formula, then there is no way you can get any x other than the index. I mean, how could you possibly know what they are? Let's say I gave you Y = [34,56,83,155]. It will assume x = [1,2,3,4]. How could it possibly know that the x I was thinking of was [2,4,6,8]? Or maybe I was thinking x was really [4,13,25,68]. There's just no way of telling the x values at all, if all you have are the Y values and no equation or actual x data.
Samar Kenkre
Samar Kenkre 2015-5-21
I do have X values that's how i plotted it, but I need a specific X value for a given Y value which isn't a part of my input data

请先登录，再进行评论。

请先登录，再回答此问题。

回答（2 个）

quicklearner
quicklearner 2015-5-21
If you have the plotted graph, then perhaps you can use the grabit.m filw ehich is available in the Matlab file exchange for free. It helps you extract data points from a graph.
All the best !
Star Strider
Star Strider 2015-5-21
‘I do have X values that's how i plotted it, but I need a specific X value for a given Y value which isn't a part of my input data’
Assuming your data meets the requirements of the interpolation functions, I would use the interp1 function. To get an x for a specific y, this will likely work:
x_new = interp1(y, x, y_new)
with x and y the data you have, and y_new the data you want the corresponding x value (here x_new) for.
  3 个评论
显示 1更早的评论
Star Strider
Star Strider 2015-5-21
One way is to force y to be monotonically increasing, then do the interpolation.
This works:
x = rand(1,10); % Create Data
y = rand(1,10); % Create Data
%
y_new = 0.5; % Known ‘y’ Value
[ys,yi] = sort(y); % Force ‘y’ To Be Monotonically Increasing
x_new = interp1(ys, x(yi), y_new);
%
figure(1)
plot(x, y, '+r')
hold on
plot(x_new, y_new, 'bp')
hold off
grid
Walter Roberson
Walter Roberson 2015-5-21
If your y is not monotonic then you have the risk that asking to look up a particular y value would return multiple results.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Creating, Deleting, and Querying Graphics Objects 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by