Whats the value of B ??

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 1

[Walter Roberson]

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]

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]

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) );

Answer 2

[Torsten]

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.