用double() 化为数值型就可以了
>> syms x
y=inline('0.579/((2*pi*0.3176)^0.5*x^1.5)*exp(-(x-0.579)^2/(2*0.3176*x))','x');
A=int(x*exp(-3*x)*y(x),x,0,inf)
double(A)
Warning: Explicit integral could not be found.
A =
int(81487005757734912/(198810802005279125*x^(1/2)*exp(3*x)*exp((625*(x - 579/1000)^2)/(397*x))), x = 0..Inf)
ans =
0.0940