零阶一类贝塞尔函数曲线及其包络线 matlab源程序「终于解决」

大家好，欢迎来到IT知识分享网。

废话不多说，请看源程序：

clear ,clc; format long x=(0:0.01:100)'; y_0=besselj(0,x); % y_1=besselj(1,x); %一阶，这里只画了0阶 % y_2=besselj(2,x); %二阶 plot(x,y_0);grid on; axis([0,100,-1,1]); title('0阶贝塞尔函数曲线图'); xlabel('Variable X'); ylabel('Variable Y'); %画包络线 hold on; [up,down] = envelope(x,y_0,'spline'); plot(x, up, 'r'); plot(x, down, 'r'); 

其中的envelope是个单独的.m文件，是个函数，用来画包络线。说白了就是求拐点然后插值：

function [up,down] = envelope(x,y,interpMethod) %ENVELOPE gets the data of upper and down envelope of the known input (x,y). % % Input parameters: % x the abscissa of the given data % y the ordinate of the given data % interpMethod the interpolation method % % Output parameters: % up the upper envelope, which has the same length as x. % down the down envelope, which has the same length as x. % % See also DIFF INTERP1 % Designed by: Lei Wang, <WangLeiBox@hotmail.com>, 11-Mar-2003. % Last Revision: 21-Mar-2003. % Dept. Mechanical & Aerospace Engineering, NC State University. % $Revision: 1.1 $ $Date: 3/21/2003 10:33 AM $ if length(x) ~= length(y) error('Two input data should have the same length.'); end if (nargin < 2)|(nargin > 3), error('Please see help for INPUT DATA.'); elseif (nargin == 2) interpMethod = 'linear'; end % Find the extreme maxim values % and the corresponding indexes %---------------------------------------------------- extrMaxValue = y(find(diff(sign(diff(y)))==-2)+1); extrMaxIndex = find(diff(sign(diff(y)))==-2)+1; % Find the extreme minim values % and the corresponding indexes %---------------------------------------------------- extrMinValue = y(find(diff(sign(diff(y)))==+2)+1); extrMinIndex = find(diff(sign(diff(y)))==+2)+1; up = extrMaxValue; up_x = x(extrMaxIndex); down = extrMinValue; down_x = x(extrMinIndex); % Interpolation of the upper/down envelope data %---------------------------------------------------- up = interp1(up_x,up,x,interpMethod); down = interp1(down_x,down,x,interpMethod); 

效果：

源程序下载：http://www.pudn.com/downloads495/sourcecode/windows/other/detail2062657.html

csdn上传资源标签里竟然没有Matlab，桑不起啊。。。。