Solve cubic equation in MATLAB

Question

PRIYANK AGARWAL 2012-3-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/33341-solve-cubic-equation-in-matlab

I need to solve a cubic equation but I don't know how to do it. Here is my coding:

    B=80.73233784;
    xc=152.01;
    R=82.05746;
    for i=1:0.1:200
        x(i)=-50+i;
        y(i)=(10^(7.23086-(1175.581/(x(i)+271.079))))*0.001315789473684;
        a(i)=y(i)/(R*x(i));
        b(i)=(4.9343*((xc/x(i))^1.5)*B)-B-((y(i)/(R*x(i)))*(B^2));
        c(i)=4.9343*((xc/x(i))^1.5)*(B^2);
        m=[a -1 b -c];
        r=roots(m);
    end

This is my equation to be solved for "v": ((a(i)*(v^3))-(v^2)+(b(i)*v)-c(i))=0;

Here "a", "b" and "c" changes with respect to "x" and "y". I want to eliminate the negative and complex roots but I am unable to do so. Moreover program shows error that roots can't be found. I am new to MATLAB and don't know much about its functions. Kindly help me. Thank you.