Integrate a polyfit-polyval in matlab, I would appreciate any input. I want to calculate the integral of the sine function from a trend li
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X=[ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 ];
Y=[ 0 0.017451121 0.034896927 0.052332105 0.069751344 0.08714934 0.104520792 0.121860412 0.139162917 0.156423038 0.173635518 0.190795114 0.207896601 0.224934771 0.241904433 0.258800419 0.275617584 0.292350805 0.308994987 0.32554506 0.341995983 0.358342746 0.374580371 0.390703911 0.406708457 0.422589134 0.438341105 0.453959573 0.469439781 0.484777014 0.4999666 0.515003915 0.529884377 0.544603456 0.559156667 0.573539579 0.587747811 0.601777035 0.61562298 0.629281427 0.642748218 0.65601925 0.669090481 0.681957931 0.694617681 0.707065874 0.719298721 0.731312494 0.743103535 0.754668253 0.766003125 0.7771047 0.787969596 0.798594504 0.808976189 0.819111488 0.828997314 0.838630657 0.848008582 0.857128234 0.865986835 0.874581687 0.882910172 0.890969753 0.898757976 0.90627247 0.913510945 0.920471196 0.927151104 0.933548635 0.939661839 0.945488856 0.95102791 0.956277314 0.96123547 0.965900868 0.970272086 0.974347793 0.978126748 0.9816078 0.984789889 0.987672046 0.990253392 0.992533143 0.994510602 0.996185169 0.997556332 0.998623675 0.999386873 0.999845692 0.999999993 ];
plot(X,Y)
p2=polyfit(X,Y,4);
p3=polyfit(X,Y,3);
hold on
c=polyval(p2,X);
plot(X,c)
FS=7;
leg = legend(["Seno","Aproximacion Seno"],'Location','northwest','Orientation','horizontal','FontSize',FS,"NumColumns",1);
x1 = 12;
x2 = 12;
leg.ItemTokenSize = [x1, x2];
legend('boxoff');
hold off![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1093975/image.jpeg)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1093975/image.jpeg)
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采纳的回答
KSSV
2022-8-11
%% Integration
p2=polyfit(X,Y,4);
fun = @(x) p2(1)*x.^4+p2(2)*x.^3+p2(3)*x.^2+p2(4)*x+p2(5) ; % using p2 from polyfit
val = integral(fun,X(1),X(end))
更多回答(1 个)
Walter Roberson
2022-8-11
https://www.mathworks.com/help/matlab/ref/polyint.html
polyint() the component vector to get the integral of the polynomial, and polyval to evaluate.
1 个评论
Walter Roberson
2022-8-12
You are not integrating sin(x), you are integrating sind(x). sind(x) = sin(alpha*x) for alpha = π/180
syms alpha x
int(sin(alpha*x), x, 0, sym(pi)/2/alpha)
ans = 1/alpha
with alpha being π/180, then 1/alpha is 180/π which is 57 point something
另请参阅
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