matlab中如何计算积分上限为无穷大的情况?

计算无穷限积分的函数，用Matlab实现。
1、函数quadFromInf用于计算从负无穷大到一个确定值a的积分
%name:quadFromInf.m
function Isum = quadFromInf(fun,a,dx0,tol,method)
if nargin < 2 ,a=0 ;end
if nargin < 3 ,dx0=0.5 ;end
if nargin < 4 ,tol = 5e-4 ;end
if nargin < 5 ,method = 1 ;end
j=0;dx = dx0;Isum = 0;x2 = a; maxint = 35;
%fprintf( j dx x2 I_j Isum );
while j<maxint
x1 = x2 - dx;
switch method
case 1, I = quad(fun,x1,x2);
case 2, I = quadl(fun,x1,x2);
otherwise, error(sprintf(method = %d not allowed,method));
end
Isum = Isum + I;
%fprintf(%4d %8.1f %8.1f %12.8f %12.8f ,j,dx,x2,I,Isum);
if j>5 & abs(I/Isum) < tol,break; end
j = j+1;x2 = x1;dx = 2*dx;
end
2、函数quadToInf用于计算从一个确定值a到正无穷大的积分。
%name:quadToInf.m
function Isum = quadToInf(fun,a,dx0,tol,method)
if nargin < 2 ,a=0 ;end
if nargin < 3 ,dx0=0.5 ;end
if nargin < 4 ,tol = 5e-4 ;end
if nargin < 5 ,method = 1 ;end
j=0;dx = dx0;Isum = 0;x1 = a; maxint = 35;
%fprintf( j dx x2 I_j Isum );
while j<maxint
x2 = x1 + dx;
switch method
case 1, I = quad(fun,x1,x2);
case 2, I = quadl(fun,x1,x2);
otherwise, error(sprintf(method = %d not allowed,method));
end
Isum = Isum + I;
%fprintf(%4d %8.1f %8.1f %12.8f %12.8f ,j,dx,x2,I,Isum);
if j>5 & abs(I/Isum) < tol,break; end
j = j+1;x1 = x2;dx = 2*dx;
end