Reflect a triangle given a mirror line

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DINESH RAMACHANDRAN on 19 Aug 2014
its three point triangle....

David Sanchez on 19 Aug 2014
Create a m-file with this function:
% line of symmetry: y = m*x + n;
Md = zeros(2,1); % Middle point between given point and its symmetric
Md(1) = (P(1) + m*P(2) - m*n)/(m^2 + 1);
Md(2) = m*Md(1) + n;
S = 2*Md - P; % symmetric point of P about given line
And this gives you the symmetric points of your triangle vertices about the symmetry line y=m*x+n:
A = [1 2];
B = [5 7];
C = [2 9];
M = [A; B; C]; % matrix to hold points
plot(M(:,1),M(:,2),'*')
m = .5;
n = -1;
x = [-100 100];
y = m.*x+n;
hold on
plot(x,y)
hold off
Ms = [As; Bs; Cs]; % matrix to hold symmetric points
hold on
plot(Ms(:,1),Ms(:,2),'r*')
hold off
axis([-10 20 -10 20])
axis square
DINESH RAMACHANDRAN on 19 Aug 2014
sir, it shows the first statement as error, i.e. Input argument "P" is undefined.

Ahmet Cecen on 19 Aug 2014
Look at householder reflectors on wikipedia. The function "flip" might also help.

Roger Stafford on 19 Aug 2014
I suggest you look at John D'Errico's advice on this kind or problem at: