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Moving from an index in the matrix to an x,y value

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Yovel
Yovel 2024-1-19
回答： Star Strider 2024-1-19
Hey
I have a 50x50 matrix that indicates points on the X,Y axis
I have some kind of function that holds the index that indicates a row and a column of some point.
My question is how do I go from an index to get the real value on the X axis and Y axis?
Let's say the indexes I got are:
row_idx=43, col_idx=3
Can I say that the value of the point is (3,7)? Or should we add 1+ to the y value? I got confused..
Thank you
  1 个评论
the cyclist
the cyclist 2024-1-19
I got confused, too.
Maybe you could post a much smaller example (say, 5x5) of your matrix. Then, what is your input, and what should the output be?

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回答（1 个）

Star Strider
Star Strider 2024-1-19
Ran in:
Perhaps something like this —
x = linspace(0, 10, 50);
y = linspace(0, 10, 50);
zm = exp(-(x-4.5).^2/4) .* exp(-(y(:)-4.5).^2/4);
[xm,ym] = ndgrid(x,y);
Zfcn = scatteredInterpolant(xm(:),ym(:),zm(:));
row_idx = 43;
col_idx = 3;
xq = interp1(x, row_idx)
xq = 8.5714
yq = interp1(y, col_idx)
yq = 0.4082
zi = Zfcn(xq,yq);
figure
surf(xm, ym, zm)
hold on
plot3(xq, yq, zi, 'rp', 'MarkerFaceColor','r', 'MarkerSize',15)
hold off
grid on
xlabel('x')
ylabel('y')
zlabel('z')
[az,el] = view
az = -37.5000
el = 30
% view(210,el)
.

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