creating for loop in fzero

2017 11 12
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更新时间：2017 11 28
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1 个投票

Dear all, I want to plot "z" vs. "kappa" where kappa is changing from 1 to 0. this is my @ff function:
function y = f(x)
y = (1/pi)*((0.1*x)-(((sqrt((1+x)./2)).*exp(1).^-(6*(sqrt(2*0.1*(1+x))))))*(kappa*(sqrt((1-x)/(1+x)))-(sqrt((1+x)/(1-x)))));
after that using fzero I want to find "z" for every single kappa in the region in order to get the plotted data:
fun = @ff; % function
x0 = 0; % initial interval
z = fzero(fun,x0);
now how can I create a loop to change kappa from 1 to 0 and get "z" for each of them on my plot. many Thanks in Advance,

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Star Strider
Star Strider 2017-11-12

1 个投票

Try this:
f = @(x,kappa) (1/pi)*((0.1*x)-(((sqrt((1+x)./2)).*exp(-(6*(sqrt(2*0.1*(1+x))))))).*(kappa*(sqrt((1-x)./(1+x)))-(sqrt((1+x)./(1-x)))));
N = 10; % Length Of ‘kappa’ Vector
kappa = linspace(0, 1, N);
for k1 = 1:N
z(k1) = fzero(@(x) f(x, kappa(k1)), 1E-3);
end
figure(1)
plot(kappa, z)
xlabel('\kappa')
ylabel('z(\kappa)')
grid

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fartash2020
fartash2020 2017-11-27
Hi again,
Now for this same equation. my Kappa is constant Kappa=0.1 I add "Delta_E" and "Lambda" to the equation and I want them to change( which I have written below). This time I want to draw a mesh plot for (Z, lambda, Delta_E). I would highly appreciate if you help me correct it:
kd = 6 ;
kappa = 0.1 ;
f = @(x,lambda) ((Delta_E)+(lambda*x)-(((sqrt((1+x)./2)).*exp(1).^(-(kd*(sqrt(2*lambda*(1+x))))))).*(kappa*(sqrt((1-x)./(1+x)))-(sqrt((1+x)./(1-x)))));
N = 100;
lambda = linspace(0.05,0.25, N);
Delta_E= linspace(0.1,0.35, N);
for k1 = 1:N
z(k1) = fzero(@(x) f(x, lambda(k1)), 1E-3);
end
figure(1)
mesh(lambda,Delta_E, z)
xlabel('\lambda')
ylabel('\delta E')
zlabel('Z')
grid
Star Strider
Star Strider 2017-11-27
I am not certain what you are doing. If you want to find the zeros of a bivariate function, I would use the contour function. See the documentation on contour for details.
However yours is trivariate in ‘lambda’, ‘Delta_E’ and ‘x’, so that might not work. You could do a nested loop through ‘lambda’ and ‘Delta_E’ using fzero. That might be the only way to approach this.
fartash2020
fartash2020 2017-11-28
Thanks Star Strider, but how can I create a nested loop?
Star Strider
Star Strider 2017-11-28
Try this:
N = 100;
kd = 6;
kappa = 0.1;
lambda = linspace(0.05,0.25, N);
Delta_E = linspace(0.1,0.35, N);
[Lm,DE] = meshgrid(lambda, Delta_E);
f = @(x,lambda,Delta_E) ((Delta_E)+(lambda*x)-(((sqrt((1+x)./2)).*exp(-(kd*(sqrt(2*lambda*(1+x))))))).*(kappa*(sqrt((1-x)./(1+x)))-(sqrt((1+x)./(1-x)))));
for k1 = 1:length(lambda)
for k2 = 1:length(Delta_E)
z(k1,k2) = fzero(@(x) f(x,lambda(k1),Delta_E(k2)), rand);
end
end
figure(1)
mesh(lambda, Delta_E, z)
You might find it worthwhile to plot the absolute value of ‘z’, because the results are complex when they are not NaN, although the plot itself reveals little.

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