MATLAB: Indices on the left side are not compatible with the size of the right side error

errormatrixmatrix array

So I'm writing code to create a matrix, M that stores various values for theta and x, but i'm unsure as to what to do about the error. Please let me know what I need to correct in order to overcome the error.

M=[];

theta=linspace(0,180,401);

x=linspace(0,10,501);

for i_theta = 1:length(theta)

for i_x = 1:length(x)

M(i_x,i_theta)= 1200*sind(theta(i_theta)) +400*cosd(theta)*x(i_x);

end

****************************************************************************

Unable to perform assignment because the indices on the left side are not compatible with the

size of the right side.

Error in Lab7 (line 9)

M(i_x,i_theta)= 1200*sind(theta(i_theta)) +400*cosd(theta)*x(i_x);

Best Answer

It's a typo in this line

M(i_x,i_theta)= 1200*sind(theta(i_theta)) +400*cosd(theta)*x(i_x);

I think it should be

M(i_x,i_theta)= 1200*sind(theta(i_theta)) +400*cosd(theta(i_theta))*x(i_x);

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MATLAB: Do I get “array indices must be positive integers or logical values” when running this for loop

Hi Spencer,

The access of i_theta in xcoord and ycoord is the issue. In MATLAB, indexing is one based.

Try to update as folllowing:

i_theta_max =100;
for i_theta = 0:i_theta_max
    theta = i_theta/(i_theta_max)*2*pi;
    xcoord(i_theta+1)=1*sin(theta); % Added 1

    ycoord(i_theta+1)=1*cos(theta); % Added 1
end
% or
i_theta_max =100;
for i_theta = 1:i_theta_max+1
    theta = (i_theta-1)/(i_theta_max)*2*pi; % Subtract 1
    xcoord(i_theta)=1*sin(theta);
    ycoord(i_theta)=1*cos(theta);
end

Hope this helps.

Regards,

Sriram

MATLAB: Solving non linear equation using fsolve

You are not passing theta_n and other parameters to root2d(). One fix is to make root2d a Nested Function. Also, you must choose a different initial point. phi0 = [10,10] worked for me.

function solve_it()
    beta_a = 10;
    alpha_n = 10 ;
    eta= 18;
    i = 18;
    theta_i = 10;
    theta_n = 10 ;
    
    fun = @root2d;
    phi0 = [10,10];
    phi = fsolve(fun,phi0);
    phi_n = phi(1),
    phi_i = phi(2),
    function F = root2d(phi)
    F = zeros(2,1);
    F(1) = (pi*sin((pi*(phi(1) + theta_n))/180)*cos((pi*phi(2))/180)*(cos((pi*theta_n)/180) + tan((pi*i)/180)*tan((pi*theta_i)/180)))/(180*sin((pi*phi(1))/180)*(cos((pi*(phi(1) + theta_n))/180)*cos((phi(2)*pi)/180) + sin((phi(2)*pi)/180)*tan((theta_i*pi)/180))^2) - (pi*cos((pi*phi(1))/180)*(cos((pi*theta_n)/180) + tan((pi*i)/180)*tan((pi*theta_i)/180)))/(180*sin((phi(1)*pi)/180)^2*(cos((pi*(phi(1) + theta_n))/180)*cos((pi*phi(2))/180) + sin((pi*phi(2))/180)*tan((pi*theta_i)/180)));
    F(2) = ((cos((pi*theta_n)/180) + tan((pi*i)/180)*tan((pi*theta_i)/180))*((pi*cos((pi*(phi(1) + theta_n))/180)*sin((pi*phi(2))/180))/180 - (pi*cos((pi*phi(2))/180)*tan((pi*theta_i)/180))/180))/(sin((pi*phi(1))/180)*(cos((pi*(phi(1) + theta_n))/180)*cos((phi(2)*pi)/180) + sin((phi(2)*pi)/180)*tan((theta_i*pi)/180))^2);
    end
end

Best Answer

Related Solutions

MATLAB: Do I get “array indices must be positive integers or logical values” when running this for loop

MATLAB: Solving non linear equation using fsolve

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