How to evaluate a unknown variable?

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Miroslav Mitev
Miroslav Mitev 2019-7-9
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
Guillaume
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.

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Peter Jarosi
Peter Jarosi 2019-7-9
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);
Learn more at https://www.mathworks.com/help/optim/ug/fsolve.html

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