how to draw the line of known slope and intercept

Question

academy25 2011-5-21

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回答： Amr Aboughazala 2022-5-6

Hello, I have a line which is in the form ax+by+c=0, with a,b and c known. In addition, I have a specific (x,y) point known, and the line should pass through it. How can I draw this line in matlab?

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Answer 1

Walter Roberson 2011-5-22

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If a*x + b*y + c = 0 then b*y = - c - a*x and then provided b is non-zero, y = -c/b - a/b * x

Then if the line is to pass through a specific (x,y) the only thing you have to worry about is ensuring that the range of x you plot includes the specific x .

For example,

x = 15:41;
y = -19/11 - (-3/2)/11 * x;
plot(x,y)

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Answer 2

Daniel Shub 2011-5-22

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I like refline

doc refline

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Answer 3

Matt Fig 2011-5-22

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You could also do it using MATLAB's polynomial functions...

% Data
a = -2;
b = 3;
c = 8;
x = 3;
y = -2/3;
% Now the plotting.
pp = [-a,-c]/b; % Polynomial as MATLAB likes it.
X = linspace(x-1,x+1);  % Where to plot the line...
pv = polyval(pp,X);  % Evaluate the polynomial.
plot(X,pv,'-b',x,y,'*r')