MATLAB: Solving system of non linear equations

Question

sym x;
sym a1;
sym a2;
sym a3;
sym a4;
sym u1;
sym u2;
sym u3;
sym u4;
u=a1+a2*x+a3*(x^2)+a4*(x^3);
l=1;
eqn=[subs(u,x,0)-u1==0,subs(diff(u(x),x),x,0)-u2==0,subs(u,x,l)-u3==0,subs(diff(u(x),x),x,l)-u4==0];
[a1, a2, a3, a4]=solve(eqn);

It is showing error.Is there anything wrong with the code?

Answer 1

Those "sym" need to be "syms"

syms x a1 a2 a3 a4 u1 u2 u3 u4

also, you need to define u as

u(x) = a1+a2*x+a3*(x^2)+a4*(x^3);