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Hello, how do I display the equation for a polyfit line on this plot?

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Charles Naegele
Charles Naegele 2018-5-17
评论： Nadir Bait Saleem 2023-11-20
if true
% code
end
p = polyfit(x,y,1);
d = polyval(p,x);
plot(x,d,'k--')
where x and y are columns of 9, averaged from 3 original sets of 9 data point columns each.
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Steven Lord
Steven Lord 2021-6-2
Ran in:
One tweak is that you can include + in the format specifier itself to avoid "+ -<number>" while displaying the sign. Look at the linear term in txt1 and txt2.
a = 2;
b = -pi;
c = exp(1);
txt1 = sprintf('y = %.4f*x^2 +%.4f*x +%.4f', a, b, c)
txt1 = 'y = 2.0000*x^2 +-3.1416*x +2.7183'
txt2 = sprintf('y = %.4f*x^2 %+.4f*x %+.4f', a, b, c)
txt2 = 'y = 2.0000*x^2 -3.1416*x +2.7183'

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采纳的回答

Image Analyst
Image Analyst 2018-5-17
Use text() to display the equation on the graph:
grid on;
% Place equation in upper left of graph.
xl = xlim;
yl = ylim;
xt = 0.05 * (xl(2)-xl(1)) + xl(1)
yt = 0.90 * (yl(2)-yl(1)) + yl(1)
caption = sprintf('y = %f * x + %f', p(1), p(2));
text(xt, yt, caption, 'FontSize', 16, 'Color', 'r', 'FontWeight', 'bold');
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更多回答（1 个）

the cyclist
the cyclist 2018-5-17
编辑：the cyclist 2018-5-17

Here is an example of how you can do this.

There are more efficient ways (e.g. using polyval on both the min and max at the same time), but I thought this might be clearer.

rng default

N = 10;
x = randn(N,1);
y = x + 0.3*randn(N,1);

p = polyfit(x,y,1);

x_min = min(x);
x_max = max(x);

d_min = polyval(p,x_min);
d_max = polyval(p,x_max);

figure
hold on
scatter(x,y)
plot([x_min x_max],[d_min d_max],'k--')
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the cyclist
the cyclist 2018-5-17
Ah, I misunderstood the question. I thought you wanted to graph the equation, and it was not working.

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