[請益] 曲線積分 trapz 值似乎會比較小?

看板MATLAB作者totemist (totem)時間9年前 (2016/03/30 18:06)推噓2(2推 0噓 3→)

留言5則, 3人參與討論串1/1

各位大大門好非常感謝上一篇在推文回答我的問題經過嘗試之後發現經由trapz之後的值都會比較小,照下組數據應該算出來結果是要大於180 X軸data是： x = 0 : 6 : 180; Y軸data是： y = [0, 1.55464981024354e-06, 5.83937700379266e-06, 1.23059070365907e-05, 2.04318517979475e-05, 2.97201993727277e-05, 3.97004137484849e-05, 4.99306499001924e-05, 6.00008482354052e-05, 6.95364018836329e-05, 7.82020677438476e-05, 8.57059548886770e-05, 9.18033097894118e-05, 9.62998878420099e-05, 9.90548056864478e-05, 9.99826536894291e-05, 9.90548056867048e-05, 9.62998878424930e-05, 9.18033097900734e-05, 8.57059548894716e-05, 7.82020677447207e-05, 6.95364018845333e-05, 6.00008482362841e-05, 4.99306499010090e-05, 3.97004137491947e-05, 2.97201993732905e-05, 2.04318517983462e-05, 1.23059070368372e-05, 5.83937700390511e-06, 1.55464981026809e-06, 0]; 方法一：基本土法煉鋼 area = zeros(1,31) for i = 1:30 area(1,i) = sqrt((y(i+1) - y(i))^2 + (x(i+1) - x(i))^2); area(1,31) = area(1,31) + area(1,j); end 算出曲線總長度答案是 area(1,31) = 1.800000000001348e+02; 方法二：用interpl內插再使用trapz積分曲線在上的弧長s=∫√(1+y'2 )dx x = 0 : 6 : 180; xi = 0 : 0.00001 : 180; yi = interpl(x, y, xi, 'spline'); plot(x, y, 'o', xi, yi); dy = diff(yi); area1 = 0.00001*trapz((1+dy.^2).^0.5); 算出曲線總長度答案是 area1 = 1.7999999e+02; 不清楚哪邊出了問題希望有大大能解惑謝謝 -- ※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 140.114.28.223 ※ 文章網址: https://www.ptt.cc/bbs/MATLAB/M.1459332411.A.72D.html