How to assign indexes to a function handle?

Question

I'm trying to approximate the integral of the functions "fun_1" and "fun_2" over the given region. In the case of one single "f" it seems ok. But I want to use a vector "f" instead of a single value to have a vector of "TL" values. I don't know how to handle this problem. The code is:

gamma = 1.4;
R = 286;
T = 273.15;
c_1 = sqrt(gamma*R*T);
c_2 = c_1
h = 0.00163;
rho_s = 2750;
M = 0;
m = rho_s*h;
eta = 0.01;
E = 72e9;
v = 0.30;
D = E*h^3/(12*(1-v^2));
f_c1 = c_1^2/(2*pi)*(m/D)^0.5;
f_c2 = c_2^2/(2*pi)*(m/D)^0.5;
n = 1500;
f = linspace(55,7700,n);
for i=1:numel(f)
    omega(i) = 2*pi*f(i);
    phi_2 = @(phi_1,beta) acos(c_2/c_1.*cos(phi_1).*(1+M.*cos(beta).*cos(phi_1)).^-1);
    tau = @(phi_1,beta) ((0.5*(rho_2*c_2/(rho_1*c_1))^0.5...
        +0.5*(rho_1*c_1/(rho_2*c_2))^0.5*sin(phi_2(phi_1,beta))./(sin(phi_1).*(1.0...
        +M*cos(beta).*cos(phi_1)))+0.5*eta*m*omega(i)*(rho_1*c_1*rho_2*c_2)...
        ^-0.5.*(f(i)/f_c2).^2.*sin(phi_1).*cos(phi_2(phi_1,beta)).^4).^2).^-1;
    fun_1 = @(phi_1,beta) tau(phi_1,beta).*sin(phi_1).*cos(phi_1);
    q_1(i) = integral2(fun_1,12*pi/180,90*pi/180,0,2*pi);
    fun_2 = @(phi_1,beta) sin(phi_1).*cos(phi_1);
    q_2 = integral2(fun_2,12*pi/180,90*pi/180,0,2*pi);
    tau_avg = q_1/q_2;
    TL = -10*log10(tau_avg);
end

Ander Biguri · Accepted Answer · 2021-09-23 15:54:00Z

1

use a cell array. TL{i}=-10*log10(tau_avg);

answered Sep 23, 2021 at 15:54

Ander Biguri

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6 Comments

Cris Luengo Over a year ago

@MohammadSd: You didn't ask about turning tau into an array, why are you indexing into tau? Please edit your question and clarify what you want to do.

Mohammad Sd Over a year ago

@CrisLuengo Thank you. Do you mean I have to ask " How to convert a function handle to an array?" so what's the answer?

Mohammad Sd Over a year ago

@AnderBiguri Thank you. But the problem is with "tau" itself. If I use tau{i} there is an error like this: "Unable to perform assignment because brace indexing is not supported for variables of this type."

Ander Biguri Over a year ago

@MohammadSd I am confused. tau is not indexable. where do you want to index it? Can you show the code that does not work, rather that the one that does work?

Cris Luengo Over a year ago

@MohammadSd I don't know. Your question sounds like you have fun_1 and fun_2, but you would like to put those in an array instead, something like fun{i}. That is where you need cell arrays. If you want "a vector of TL values", and TL is currently a scalar, then what is stopping you from doing TL(i) = -10*log10(tau_avg);?

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Mohammad Sd · Accepted Answer · 2021-09-24 07:22:54Z

0

I received this answer from a user in MATLAB Answers that worked for me and solved my problem. So the vectorized version compared to the loop is more efficient.

... the integral2 function cannot integrate arrays, although integral can. The way to deal with that problem with respect to a double integral is essentially:

f = randn(1, 25);
fcn = @(x,y) sin(2*pi*f.*x) .* exp(0.1*f.*y);
int2 = integral(@(y) integral(@(x) fcn(x,y), 0, 1, 'ArrayValued',1), -1, 0, 'ArrayValued',1);

This returns a vector the size of f.

answered Sep 24, 2021 at 7:22

Mohammad Sd

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