logical index issue in for lloop

syms x t real
mu=(1/16)^4
m=(cos(x)+1i*sin(x))/(1+((1/mu)^4-1)*(cos(4*t)+1i*sin(4*t)));
n=real(m)
x=0.2:0.2:0.8
t=0.1:0.4:0.9
u=zeros(1);
row=0
for i=1:length(x)
    row=row+1
    col=0;
    for j=1:length(t)
        col=col+1
        u(row,col)=n(x(i),t(j))
        
    end
end

why it is showing the below error .

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in indexing (line 936)

R_tilde = builtin('subsref',L_tilde,Idx);

According to my logic row index will be one and colum will be also one and loop will run upto length of x and t

Answer 1

[Walter Roberson]

syms x t real
mu=(1/16)^4

mu = 1.5259e-05

m=(cos(x)+1i*sin(x))/(1+((1/mu)^4-1)*(cos(4*t)+1i*sin(4*t)));
n=real(m)
disp(char(n))

(cos(x)*(18446744073709551616*cos(4*t) + 1))/((18446744073709551616*cos(4*t) + 1)^2 + 340282366920938463463374607431768211456*sin(4*t)^2) + (18446744073709551616*sin(4*t)*sin(x))/((18446744073709551616*cos(4*t) + 1)^2 + 340282366920938463463374607431768211456*sin(4*t)^2)

So n is a scalar value.

u(row,col)=n(x(i),t(j))

But there you are asking to index n at location x(i) and t(j) . x(i) and t(j) are not integers, so you get an error about indexing at non-integers. If x(i) and t(j) did happen to be integers, you would probably have gotten an error about attempting to index out of range, since n is a scalar.

The cure is to write,

n(x,t) = real(m)

which will declare n as a symbolic function of two variables.