How to call specific number from polyfit

Question

Anastasia Zistatsis 2021-3-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/770208-how-to-call-specific-number-from-polyfit

回答： David Hill 2021-3-11

Hello,

How does one call a specific number from the polyfit below? I'd like to do O27fifth = p(27), but this does not work/isn't right.

T = [0 8 16 24 32 40];
Oxy = [14.621 11.843 9.870 8.418 7.305 6.413];
p = polyfit(T,Oxy, 5);
figure(2)
plot(t,polyval(p,t))
title('fifth order polynomial')
%need Oxy when T = 27
%sfprintf('Oxy(27) = %0.41f\n',O27fifth);

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Answer 1

Star Strider 2021-3-11

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/770208-how-to-call-specific-number-from-polyfit#answer_645503

在 MATLAB Online 中打开

Try this:

T = [0 8 16 24 32 40];
Oxy = [14.621 11.843 9.870 8.418 7.305 6.413];
p = polyfit(T,Oxy, 5);
pv27 = polyval(p,27);
figure(2)
plot(T,polyval(p,T),  27,pv27,'xr')
title('fifth order polynomial')
text(27,pv27, sprintf('(%d, %.2f)\n\\downarrow',27,pv27),'vert','bottom','horiz','left')

.

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Answer 2

David Hill 2021-3-11

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/770208-how-to-call-specific-number-from-polyfit#answer_645508

在 MATLAB Online 中打开

T = [0 8 16 24 32 40];
Oxy = [14.621 11.843 9.870 8.418 7.305 6.413];
p = polyfit(T,Oxy, 5);
figure(2);
plot(T,Oxy,0:.1:40,polyval(p,0:.1:40));
pAt27=polyval(p,27);