Polyfit, polyval and plot
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I am trying to fit the polynomials to the data with 0,1,2 degrees respectively and plot them on the same graph. I wonder why there is only one line shown on the plot which is the 0 degree polynomial.
y = flip(AdjClose).'
x = 1:503;
polyfit(y,x,0);
coef1 = polyfit(y,x,0);
y1 = polyval(coef1,x);
hold on
plot(x,y);
plot(x,y1);
polyfit(y,x,1);
coef2 = polyfit(y,x,1);
y2 = polyval(coef2,x);
plot(x,y2);
polyfit(y,x,2);
coef3 = polyfit(y,x,2);
y3 = polyval(coef3,x);
plot(x,y3);
采纳的回答
the cyclist
2016-2-16
Because the syntax should be
polyfit(x,y,N)
and not
polyfit(y,x,N)
Here is some code that illustrates the fix:
x = 1:503;
y = 250 + 0.02*x + 0.005*x.^2 + 0.2*rand(1,503).*x;
figure polyfit(y,x,0); coef1 = polyfit(x,y,0); y1 = polyval(coef1,x); hold on plot(x,y,'.'); plot(x,y1); polyfit(x,y,1); coef2 = polyfit(x,y,1); y2 = polyval(coef2,x); plot(x,y2); polyfit(y,x,2); coef3 = polyfit(x,y,2); y3 = polyval(coef3,x); plot(x,y3);
5 个评论
Jovos
2016-2-16
编辑：the cyclist
2016-2-16
the cyclist
2016-2-16
It's difficult to know the problem without being able to run your code. Can you post a *.mat file with the value of AdjClose?
Jovos
2016-2-17
the cyclist
2016-2-17
It's because your last y value is NaN, which is causing the fitted coefficients to all be NaN, and therefore unplottable.
Put the lines
x(end) = [];
y(end) = [];
in your code before the first fit, and you will see results.
Jovos
2016-2-18
更多回答（1 个）
Walter Roberson
2016-2-17
0 个投票
When you use "hold on" before you have done any plotting, your xlim and ylim are frozen at their default values, which are [0 1] and [0 1]. If your plotting goes outside that range then nothing will show up. You should delay the "hold on" until after the first plot is done.
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