Error using mupadmex of syms

in th file here that is attached, this is the program that i am trying to run:

 syms t
syms j
  K(t)=exp(-t);
  F=1;
   integrand(t,j) = K(t-j)*F;
   U(t)=1 - int(integrand(t,j),j,0,t);
l=1;
h=l/10;
n=round(l/h);
Utest=zeros(1,n+3);
Uapp=zeros(1,n+3);
Kvector= zeros(1,n+3);
Fvector= zeros(1,n+3);
Integvector= zeros(1,n+3);
for i=1:n+1
Integvector(i)=int(integrand(t,j),j,(i-1)*h,i*h);
end;

then i get the following error:

"The following error occurred converting from sym to double: Error using mupadmex 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."

why is that? how can i correct it so it will work right?

Answer 1

[Ced]

In your second to last line

Integvector(i)=int(integrand(t,j),j,(i-1)*h,i*h);

the left side is a double vector because you initialized Integvector as such, whereas the right side is a symbolic expression still dependent on t.

So, either you initialize Integvector as a symbolic variable instead of a double vector, or you make the right side into a double by assigning a value to "t". This could be done using "subs".