Reusing a calculated variable twice?

Question

Joshua 2014-3-12

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/121269-reusing-a-calculated-variable-twice

编辑： Marta Salas 2014-3-12

Hi all, I'm trying to run a series of calculations with multiple variables used multiple times to collect different values. So far I have this:

clear
g=9.81;
h=10;
u=1.5;
syms a b c d
a=u./sqrt(g.*h)
h=10;
d=0.5;
c=0.5;
b=solve(((a^(2).*b^4)/2)+2.*c.*a^(2).*b^(3)-(2-2.*d+a^(2)).*b^(2)-(4.*c+2.*c.*a^(2)-4).*b+((a^(2)/2)+4.*c-2.*c^(2).*d-2),b,'MaxDegree',3);
x=b(find(b>1))
e1=((2.*(x(1)+c))-((x(1)-1)^3)/(d.*x(1).*(x(1)-c)))/(4+((((x(1))^(2))-1)/(c.*x(1))))
e2=((2.*(x(2)+c))-((x(2)-1)^3)/(d.*x(2).*(x(2)-c)))/(4+((((x(2))^(2))-1)/(c.*x(2))))
if (e1>c)
    if (1>e1)
    f1=(x(1))^2-e1^2
    end
end
if (e2>c)
    if(1>e2)
    f2=(x(2))^2-e2^2
    end
end
g=f2/(e2)^2
syms h1 a d f2
h1=solve(((h1^3)./2)-((3/2).*h1^2)+(1-a^2+(f2.*d.*(a^2))./2).*h1-((f2.*d.*(a^2))/2),h1,'MaxDegree',3)

The code works as expected except the last line in which it gives me 3 answers in terms of a rather than a numerical answer. How do I make it reuse the value calculated for a like it did so in the initial solve line? Many thanks

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Answer 1

Marta Salas 2014-3-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/121269-reusing-a-calculated-variable-twice#answer_128048

编辑：Marta Salas 2014-3-12

在 MATLAB Online 中打开

when you use "syms" is to create symbolic variables.

clear
g=9.81;
h=10;
u=1.5;
syms a b c d 
a=u./sqrt(g.*h)
h=10;
d=0.5;
c=0.5;

you are not using these symbolic variables (a b c d) because you assigned values to them. So, remove the "syms" lines, you will get a numeric solution.

NOTE: to get a numeric solution you will need to assign first the value of h1, which in you previous code is not defined.