Whats the value of B ??

Asked by mr mo

mr mo (view profile)

on 10 Jun 2016
Latest activity Commented on by Walter Roberson

Walter Roberson (view profile)

on 10 Jun 2016
Accepted Answer by Walter Roberson

Walter Roberson (view profile)

Hello every one.
I wanna find the value of B, that make the variable Z=0.8 or very close to 0.8. How can I do that in Matlab ?
here is the sample of my code .
n=10;
C=[0.2 0.55 0.7 0.8 0.99 0.1 0.24 0.33 0.44 0.74];
P=exp(-B*C);
P=P/sum(P);
z = sum (P(1 : n/2));
With best regards.

Answer by Walter Roberson

Walter Roberson (view profile)

on 10 Jun 2016

syms B
n = 10;
C = [0.2 0.55 0.7 0.8 0.99 0.1 0.24 0.33 0.44 0.74];
P = exp(-B.*C);
P2 = P./sum(P);
z = sum(P2(1 : n/2));
Bval = vpasolve(z == 0.8,B);
However, this will give only one of the 89 solutions. It happens to be the only real-valued solution so that might be good enough for you.

mr mo

mr mo (view profile)

on 10 Jun 2016
Thanks for your help
But I want to use the variable B in the Next other lines of my code, and here the variable B becomes symbolic, How can I use B in other lines ?? with best regards
Walter Roberson

Walter Roberson (view profile)

on 10 Jun 2016
If you construct the other lines symbolically in B then use
subs(expression, B, Bval)
If the other lines expect B numerically, then use
syms Bs
n = 10;
C = [0.2 0.55 0.7 0.8 0.99 0.1 0.24 0.33 0.44 0.74];
P = exp(-Bs.*C);
P2 = P./sum(P);
z = sum(P2(1 : n/2));
B = double( vpasolve(z == 0.8, Bs) );

Torsten (view profile)

on 10 Jun 2016

function main
x0=1;
sol=fzero(@fun,x0)
function y=fun(x)
n=10;
C=[0.2 0.55 0.7 0.8 0.99 0.1 0.24 0.33 0.44 0.74];
for k=1:length(x)
xk=x(k);
P=exp(-xk*C);
P=P/sum(P);
y(k)=0.8-sum(P(1:n/2));
end
Best wishes
Torsten.