Mapping 1D vector to 2D area

Question

Prasanna Routray 2024-9-27，10:27

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2155865-mapping-1d-vector-to-2d-area

评论： Cris LaPierre 2024-9-30，12:56

采纳的回答： Cris LaPierre

load xPoints; load yPoints; j=boundary(xPoints,yPoints,0.1); Plot(xPoints(j),yPoints(j))

%How do I map the x-values to y-values here?

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Prasanna Routray 2024-9-27，11:23

Hi Rahul,

I want to get a set of points that map to a particular x-value.

The boundary actually forms an area.

I want to get a function or method so that whenever I get an 'x', I should be able to get a set of y-values.

Hope that make the question clear. The forum was having an issue with server so, posted it from my phone.

Image Analyst 2024-9-27，16:59

What if, for a given vertical line (like you specified x with some specific value), there are no y values for that exact x value? Maybe some are close but not exact. Do you want to find all y values within a certain tolerance of your specified x? If so use ismembertol().

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Answer 1

Cris LaPierre 2024-9-27，12:11

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2155865-mapping-1d-vector-to-2d-area#answer_1523720

在 MATLAB Online 中打开

Are you wanting all the corresponding yPoints, or just those on the boundary?

load xPoints; 
load yPoints; 
j=boundary(xPoints,yPoints,0.1); 

To me, the simplest approach is to find the indices of the desired X value, and use that the extract the corresponding Y values.

idx = xPoints==2;
yPoints(idx)
ans = 5×1
    0.0016
    0.0015
    0.0015
    0.0014
    0.0014
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That will return all points. If you just want them from the boundary, try this.

ids = xPoints(j)==2;
yPoints(j(ids))
ans = 0.0014

Here, only one value is returned because only one X value in boundary exactly equals 2. In that case, you could use ismembertol.

LIA = ismembertol(xPoints(j),2,0.01);
yPoints(j(LIA))
ans = 2×1
    0.0013
    0.0014
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Prasanna Routray 2024-9-30，6:01

Cris, i accept this answer because we have to look for a workaround for this. This works for the timebeing as I'm fixing the boundary.

Thanks..

Cris LaPierre 2024-9-30，12:56

Feel free to submit an enhancement suggestion on the feature you would like to MathWorks here: https://www.mathworks.com/support/contact_us.html

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Answer 2

Rahul 2024-9-27，14:52

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2155865-mapping-1d-vector-to-2d-area#answer_1523795

在 MATLAB Online 中打开

Hi @Prasanna Routray,

I believe that you're trying to want to obtain a reverse mapping, from xPoints data to yPoints data, using a MATLAB function. Here's how you can code the same:

function [res_x, res_y] = getYs(x, xPoints, yPoints)
    x = 5;
    n = size(xPoints, 1);
    res_y = [];
    res_x = [];
    for i=1:n
        if xPoints(i) == x
            res_y = [res_y yPoints(i)];
            res_x = [res_x x];
        end
    end
end

Use the above function to get yPoints values corresponding to a given 'x', plot the resultant values on the figure, and display the resultant array 'res_y':

load xPoints; load yPoints; 
j=boundary(xPoints,yPoints,0.1); 
plot(xPoints(j),yPoints(j), 'Color','black');
hold on;
% Call getYs to get corresponding y values for a given x = 5
x = 5;
[res_x, res_y] = getYs(x, xPoints, yPoints);
% Plot returned data using dotted red line on same graph
plot(res_x, res_y, 'r.');
disp(res_y);
hold off;

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Prasanna Routray 2024-9-30，5:59

Hi Rahul,

I have been trying to do reverse mapping. however, I'm looking for a set of points and not just the boundary points as I posted in one of the replays.

Thanks

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