Why am I not getting the m array?

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Mariam Shahab 2022-10-1

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https://ww2.mathworks.cn/matlabcentral/answers/1815580-why-am-i-not-getting-the-m-array

评论： Mariam Shahab 2022-10-1

采纳的回答： Star Strider

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Hi all,

I have the following function:

function [m,yinter] = radial_lines(X,Y,xi,yi)
if X==Y
    m=inf;
    yinter= X;
   return
end
% Calculate the slope:
m = (Y - yi)./((X) - xi);
% Solve for y-intercept
yinter = yi - m.*xi;
fplot(yinter)
end
%% data
X=[6,7,10,14,13,9];
Y=[12,9,7,8,10,14];
xi=10;
yi=10;

The issue i am running into is that when using the radial_lines function, I get a plot with horizontal lines. However I need the lines to have a slope. I am not quite sure what i am doing wrong when calculating the slopes. I should be getting an arry of m values but the code does not give me that output. Can some one kinldy help me out? Thanks.

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Torsten 2022-10-1

编辑：Torsten 2022-10-1

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Slope and y-intercept can be obtained from my answer given below.

X=[6,7,10,14,13,9];

Y=[12,9,7,8,10,14];

xi=10;

yi=10;

hold on

for i=1:6

plot([X(i),xi],[Y(i),yi])

end

hold off

Mariam Shahab 2022-10-1

Thank you for your help. This is the graph I was aimming for.

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Answer 1

Star Strider 2022-10-1

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That clears up much.

Plotting them is simply this —

%% data

X=[6,7,10,14,13,9];

Y=[12,9,7,8,10,14];

xi=10;

yi=10;

figure

plot([ones(size(X))*xi; X], [ones(size(Y))*yi; Y], '-k')

grid

axis([5 15 6 15])

axis('equal')

text(X*1.01,Y*1.01,compose('(%2d,%2d)',[X;Y].'))

It is not necessary to plot the individual regressions, although you can certainly do that if you want to. Getting the slopes and intercepts may be enough, and your function does that.

.

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Answer 2

Torsten 2022-10-1

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https://ww2.mathworks.cn/matlabcentral/answers/1815580-why-am-i-not-getting-the-m-array#answer_1064655

编辑：Torsten 2022-10-1

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yinter is not a function. So use "plot" instead of "fplot" (whatever abscissa data you might want to choose).

Not that yinter(3) = Inf which is not plotted.

%% data
X=[6,7,10,14,13,9];
Y=[12,9,7,8,10,14];
xi=10;
yi=10;
[m yinter] = radial_lines(X,Y,xi,yi)
m = 1×6
   -0.5000    0.3333       Inf   -0.5000         0   -4.0000
yinter = 1×6
   15.0000    6.6667       Inf   15.0000   10.0000   50.0000
function [m,yinter] = radial_lines(X,Y,xi,yi)
  for i=1:numel(X)
    if X(i)==xi
      m(i)=inf;
      yinter(i)= inf;
    else
      % Calculate the slope:
      m(i) = (Y(i) - yi)/(X(i) - xi);
      % Solve for y-intercept
      yinter(i) = Y(i) - m(i)*X(i);
    end
  end
end