My First Derivative is not correctly calculated in matlab

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inzamam shoukat
inzamam shoukat 2024-3-21
评论： inzamam shoukat 2024-3-21
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

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Bruno Luong
Bruno Luong 2024-3-21
编辑：Bruno Luong 2024-3-21
Ran in:
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 = 

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Manikanta Aditya
Manikanta Aditya 2024-3-21
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!

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