How to evaluate a unknown variable?

Question

Miroslav Mitev 2019-7-9

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/470898-how-to-evaluate-a-unknown-variable

评论： Peter Jarosi 2019-7-10

I am trying to evaluate a specific variable, i.e., lambda from the following expression:

alpha=0.9;
g=[3, 2, 1];
N=10;
P=5;
sum(( lambda*(2-alpha)-sqrt(lambda*alpha*(lambda*alpha+g.*4*(1-alpha))) ) ./ ( g.*2*lambda*(alpha-1) )) = N*P

Which function shall I use to find the value of lambda that satisfies the equality above, since it is the only unknown variable?

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Guillaume 2019-7-9

You could use fzero if your equation made sense. On the left side of your equation you have a 3 element vector (with 3 different values obviously). On the right hand side you have a scalar.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Peter Jarosi 2019-7-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/470898-how-to-evaluate-a-unknown-variable#answer_382557

在 MATLAB Online 中打开

Using fsolve:

alpha=0.9;
g=[3, 2, 1];
N=10;
P=5;
f = @(lambda) sum(( lambda*(2-alpha)-sqrt(lambda*alpha*(lambda*alpha+g.*4*(1-alpha))) ) ...
    ./ ( g.*2*lambda*(alpha-1) )) - N*P;
lambda0 = 1;
options = optimoptions('fsolve','Display','iter','Algorithm','levenberg-marquardt');
lambda = fsolve(f, lambda0, options);