how can i use for loop for this script

for b=1:1:1200    
    omega(b)=b;
    Omega(b)=omega(b)*2*pi;
alpa=-(roh*omega(b)^2/E)-(roh*omega(b)/k*G);
    beta=-(roh*A*omega(b)^2/E*I)-(roh^2*omega(b)^4/E*k*G);
for j=1:4 
    k_j(b) =(-1)^(j(b)/2)*([sqrt(alpa+(-1)^j(b))*sqrt((alpa)^2+4*beta)/2]);
    k1(b)=k_j(b);
    k2(b)=k_j(b);
    k3(b)=k_j(b);
    k4(b)=k_j(b);

[DGM]

I doubt this needs any loops at all, but then there's this thing.

k_j(b) =(-1)^(j(b)/2)*([sqrt(alpa+(-1)^j(b))*sqrt((alpa)^2+4*beta)/2]);

What's j(b) supposed to be? j is a scalar.

[shoaib Shoaib]

here i use two loops in one code the one is for b=1:1:1200 and the other is for j=1:4

[shoaib Shoaib]

i dont know how to get the value of k1(b), k2(b), k3(b) ,k4(b)

[DGM]

I see that there are loops. I asked what j(b) is supposed to be. The variable j is a scalar within the scope of the inner loop. You are trying to find j(1:1200). There is no j(2), let alone j(1200). I don't understand what you're trying to do with this expression.

Also: is Omega different than omega, or is that a typo?

This doesn't appear to need any loops. Just use two orthogonal vectors, and your results will be 1200x4

b = (1:1200).';
roh = 0.1;
A = 1;
E = 1;
k = 1; 
G = 1; 
I = 1; 

omega = 2*pi*b; % i'll assume that Omega is a typo
alpa = -(roh*omega.^2/E)-(roh*omega/k*G);
beta = -(roh*A*omega.^2/E*I)-(roh^2*omega.^4/E*k*G);
	
j=1:4;
% this whole expression makes no sense
%k_j =(-1)^(j(b)/2)*([sqrt(alpa+(-1)^j(b))*sqrt((alpa)^2+4*beta)/2]);

% if we assume j(b) can be replaced with j
k_j = (-1).^(j/2) .* sqrt(alpa + (-1).^j) .* sqrt(alpa.^2 + 4*beta)/2;

% i guess these are just placeholders?
k1=k_j;
k2=k_j;
k3=k_j;
k4=k_j;

[shoaib Shoaib]

no i dont want to find j(1:1200) i have to find the value of k1..k4 from the expression

k_j = (-1).^(j/2) .* sqrt(alpa + (-1).^j) .* sqrt(alpa.^2 + 4*beta)/2;

using for loop j=1:4 as this possible, i dont understand how to write this in code, actually k1(b),k2(b),k3(b),k4(b) is matrix element such as

T1=zeros(4,4);

T1(1,1)=k1(b)^-3;

T1(1,2)=k2(b)^-3;

T1(1,3)=k3(b)^-3;

T1(1,4)=k4(b)^-3;

i get this error

% Error in MuPAD command: DOUBLE cannot convert the input expression into a double array.

If the input expression contains a symbolic variable, use the VPA function instead.

Answer 1

[Sambit Supriya Dash]

As per your given expression in the question,

the assumptions of the constants here taken as 1,

The running code is,

roh = 1; A = 1; E = 1; I = 1; k = 1; G = 1;

for b = 1:1200
    omega(b) = b;
    Omega(b) = omega(b)*2*pi;
    alpa(b) = -(roh*omega(b)^2/E)-(roh*omega(b)/k*G);
    beta(b) = -(roh*A*omega(b)^2/E*I)-(roh^2*omega(b)^4/E*k*G);
     
    for j = 1:4
        k_j =(-1)^(j/2)*((sqrt(alpa(b)+(-1)^j)*sqrt((alpa(b))^2+4*beta(b))/2));        
        k1(b)=k_j;
        k2(b)=k_j;
        k3(b)=k_j;
        k4(b)=k_j;
    end 
end

And the symbolic solution would be,

syms roh A E I k G
for b = 1:1200
    omega(b) = b;
    Omega(b) = omega(b)*2*pi;
    alpa(b) = -(roh*omega(b)^2/E)-(roh*omega(b)/k*G);
    beta(b) = -(roh*A*omega(b)^2/E*I)-(roh^2*omega(b)^4/E*k*G);
     
    for j = 1:4
        k_j =(-1)^(j/2)*((sqrt(alpa(b)+(-1)^j)*sqrt((alpa(b))^2+4*beta(b))/2));        
        k1(b)=k_j;
        k2(b)=k_j;
        k3(b)=k_j;
        k4(b)=k_j;
    end    
end

Hope this helps....

Answer 2

[Sambit Supriya Dash]

k_j(b) =(-1)^(j(b)/2)*([sqrt(alpa+(-1)^j(b))*sqrt((alpa)^2+4*beta)/2]);

Provide the original formula in a text or written manner (not the typed one). Then, I will guide you further.

[shoaib Shoaib]

this is the orignal formula

[Sambit Supriya Dash]

Following this document,

https://www.mathworks.com/matlabcentral/answers/822770-how-can-i-use-for-loop-for-this-script#answer_693600

this answer fits well.

Answer 3

[Sambit Supriya Dash]

According to your given document,

As per this formula,

Your parameters in the code should be,

alpha(b) = -((rho*w^2)/E)-((rho*w^2)/(k*G));
beta(b) = -((rho*A*w^2)/(E*I))-(((rho^2)*w^4)/(E*k*G));
k_j(b) = (-1^(j*0.5))*sqrt(((alpha(b)+((-1^j)*(sqrt(((alpha(b))^2)+(4*beta(b)))))))*0.5);

For Symbolic Calculations,

syms rho A E I k G

for b=1:1200    
    omega = b;
    w = omega*2*pi;
    alpha = -((rho*w^2)/E)-((rho*w^2)/(k*G));
    beta = -((rho*A*w^2)/(E*I))-(((rho^2)*w^4)/(E*k*G));
    for j=1:4 
        k_j(b) = (-1^(j*0.5))*sqrt(((alpha+...
            ((-1^j)*(sqrt(((alpha)^2)+(4*beta))))))*0.5);
    end
    k1=k_j;
    k2=k_j;
    k3=k_j;
    k4=k_j;
end

For specific values of the parameters,

rho = 1; A = 1; E = 1; I = 1; k = 1; G = 1;

for b=1:1200    
    omega = b;
    w = omega*2*pi;
    alpha = -((rho*w^2)/E)-((rho*w^2)/(k*G));
    beta = -((rho*A*w^2)/(E*I))-(((rho^2)*w^4)/(E*k*G));
    for j=1:4 
        k_j(b) = (-1^(j*0.5))*sqrt(((alpha+...
            ((-1^j)*(sqrt(((alpha)^2)+(4*beta))))))*0.5);
    end
    k1=k_j;
    k2=k_j;
    k3=k_j;
    k4=k_j;
end

Hope this works good.