solving system of non linear equations

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naveen badri
naveen badri 2016-11-15
评论： naveen badri 2016-11-15
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?

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Walter Roberson
Walter Roberson 2016-11-15
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);
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Walter Roberson
Walter Roberson 2016-11-15
[a1, a2, a3, a4]=solve(eqn, a1, a2, a3, a4);
It was solving for the u variables by default.

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