calculation error in hyperbolic function

syms x

syms t

U=zeros(1,2,'sym');

A=zeros(1,2,'sym');

B=zeros(1,2,'sym');

C=zeros(1,2,'sym');

series(x,t)=sym(zeros(1,1));

U(1)=(tanh(x))^2

for k=1:3

A(1)=0;

B(1)=0;

C(1)=0;

for i=1:k

A(1)=simplify(A(1)+diff( U(i),x,1)*diff(U(k-i+1),x,1));

B(1)=simplify(simplify(B(1)+U(i)*diff(U(k-i+1),x,2)));

for j=1:i

C(1)=simplify(C(1)+U(j)*U(i-j+1)*diff(U(k-i+1),x,1));

end

end

U(k+1)=(-2*C(1)+(1/2)*B(1)+A(1))/k;

end

for k=1

series(x,t)=(series(x,t)+U(k)*power(t,k-1));

end

series

row=0

C2=zeros(1);

for r=1

row=row+1;

col=0;

e=(r-11)

for t=1

col=col+1;

f=((t)/1000);

C2(row,col)=series(e,f);

end

end

For k=1 the solution is (tanh(x))^2 and using the loop if i evaluate the value for x=-10 the answer is 0.999999999 .But if directly put the value of x=-10 in (tanh(x))^2 the value is -1 .Why this difference appear?

Answer 1

[David Goodmanson]

one possibility:

(tanh(-10))^2
ans =  1.0000         % correct

although

tanh(-(10)^2)         % traveling parenthesis
ans = -1

[yogeshwari patel]

What is traveling parenthesis ? How should I correct it in my MATLAB code

[David Goodmanson]

Hi yp,

what I meant was, as I understand the problem the first expression (used in the loop) is correct, and the second expression is incorrect. The second expression is a totally different function because the parenthesis is in a different place. I am speculating about what went wrong, and the second expression might not be what you used, but it does have the "correct incorrect answer" of -1.