How to make MuPAD know a limit is zero?

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Mike 2015-11-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/255513-how-to-make-mupad-know-a-limit-is-zero

When I type in the following code, MuPAD returns a complicated answer that includes the limit as x approaches negative infinity. How do I get it to realize that the quantity it returns labelled sigma3 is zero. I thought that by defining Ws and rho as real and positive it would realize this.

Thanks

    reset();    
    assume(U, Type::Real and Type::Positive);    
    assume(Wc, Type::Real and Type::Positive);
    assume(Ws, Type::Real and Type::Positive);
    assume(`&rho;`, Type::Real and Type::Positive);
    A:=cos(2*U)+((Wc)/U)*sin(2*U);
    B:=exp((Ws/`&rho;`)*(x+(2*`&rho;`)));
    C:=cos(Q*((x/`&rho;`)+2));
    S:=sin(Q*((x/`&rho;`)+2));
    F:=U*sin(2*U)-Wc*cos(2*U);
    G:=A*B*(A*C+((1/Q)*F*S));
    R:=int(G, x=-infinity..(-2*`&rho;`),IgnoreAnalyticConstraints);