My First Derivative is not correctly calculated in matlab

syms yApprox(X1) a0 a1 a2 a3 a4 a5 a6

yApprox = a0 + a1.*X1 + a2.*(X1).^2 + a3.*(X1).^3+ a4.*(X1).^4 + a5.*(X1).^5 + a6.*(X1).^6;

BC1= subs(yApprox,X1,0)

BC2 =subs((diff(yApprox)),X1,0) %The answer is suppose to be a1 but instead of that i got 1

Answer 1

[Bruno Luong]

syms yApprox(X1) a0 a1 a2 a3 a4 a5 a6
yApprox = a0 + a1.*X1 + a2.*(X1).^2 + a3.*(X1).^3+ a4.*(X1).^4 + a5.*(X1).^5 + a6.*(X1).^6;

BC1= subs(yApprox,X1,0) 

BC1 = 

BC2 =subs((diff(yApprox,X1)),X1,0) % pay attention to diff(..)

BC2 = 

[inzamam shoukat]

thanks alot

Answer 2

[Manikanta Aditya]

Hey,

Looks like the issue you are encountering is due to the differentiation operation. When you differentiate 'yApprox' with respect to X1, the coefficient a1 is treated as a constant, and the derivative of X1 with respect to X1 is 1. That’s why you’re getting 1 instead of a1.

syms X1 a0 a1 a2 a3 a4 a5 a6
yApprox = a0 + a1.*X1 + a2.*(X1).^2 + a3.*(X1).^3+ a4.*(X1).^4 + a5.*(X1).^5 + a6.*(X1).^6;
BC1= subs(yApprox,X1,0);

diff_yApprox = diff(yApprox, X1);
BC2 = subs(diff_yApprox, X1, 0);

In this code, 'diff_yApprox' is the derivative of 'yApprox' with respect to X1. When X1=0 is substituted into 'diff_yApprox', the result should be a1 as expected.

Thanks!

[inzamam shoukat]

thanks alot