Finding the equation of a line passing 2 points
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Soroush Asarzadeh
am 16 Jul. 2016
Kommentiert: Image Analyst
am 29 Jan. 2023
Hello, I have two points (x1,y1) and (x2,y2). Now I want to find the linear equation of a line passing through these 2 points. The equation must be like f(x)=a*x+b. Is there any function in matlab that accepts coordinates of two points an gives the related linear equation back? If not, I know that a=(y2-y1)/(x2-x1) but what is the short and easy way to find 'b'? Thanks in advance!
1 Kommentar
Ahmed
am 27 Dez. 2021
You can select Polynomial of degree 1 from the cftool
this will give you something like this
Linear model Poly1:
f(x) = p1*x + p2
Coefficients:
p1 = xx
p2 = xx
where xx could be any number
Akzeptierte Antwort
Image Analyst
am 16 Jul. 2016
Try polyfit:
coefficients = polyfit([x1, x2], [y1, y2], 1);
a = coefficients (1);
b = coefficients (2);
5 Kommentare
Image Analyst
am 27 Nov. 2022
@Jose then define it. Certainly you must know what points you fit the line through. So, what variable names did you use? Use those instead of x1, etc.
Weitere Antworten (3)
Star Strider
am 16 Jul. 2016
A third (and probably the most efficient) option for this particular problem:
x = [1 2];
y = [5 4];
c = [[1; 1] x(:)]\y(:); % Calculate Parameter Vector
slope_m = c(2)
intercept_b = c(1)
slope_m =
-1
intercept_b =
6
This uses the mldivide,\ operator to do a least-squares fit of the points.
2 Kommentare
Alok Mishra
am 15 Sep. 2022
Bearbeitet: Alok Mishra
am 15 Sep. 2022
function [a b c eq] = makeEquationFrom2Points(x1,y1,x2,y2) syms x y; if x1==x2 && y1==y2 disp('Need 2 distinct points'); a=NaN; b=NaN; c=NaN; eq="null"; return; else if x1==x2 b=0; a=1; c=x1; else %for lines m not_equal to inf %y=mx+c %m is coeff(1) and coeff(2) is c coefficient=polyfit([x1 x2],[y1 y2],1); a=-coefficient(1); c=coefficient(2); b=1; end eq=a*x+b*y==c; end
on workspace do:
[a b c eq]=makeEquationFrom2Points(1,2,3,4)
Output: a =
-1.0000
b =
1
c =
1.0000
eq =
y - x == 1
3 Kommentare
Image Analyst
am 29 Jan. 2023
@navid seif put the function in a loop over x1
for k = 1 : numel(x1)
if x1(k) == x2(k) && y1(k) == y2(k)
% etc.
end
end
Everything should have an index k, like a(k), b(k), etc., so that you store the results for every set of data.
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