Can not calculate coefficient Accurately

My equation is

Disp =X1*(4*X2 - 4*X1 + 1)

I am using Fallowing Command

[EQ_01, T] =coeffs(Disp , [X1 X2])

N1 = EQ_01(1) by using this cammand i got fallowing answer

N1 = -4

My required answer is 1 - 4X1

N2 = EQ_01(2) by using this cammand i got fallowing answer

N2 =4

My required answer is

4X1

Answer 1

[Lokesh]

Hi inzamam,

As per my understanding, the values of coefficients returned from 'coeffs' is different from your expected values.

Given your equation 'Disp =X1*(4*X2 - 4*X1 + 1)' and the MATLAB command '[EQ_01, T] =coeffs(Disp , [X1 X2])' , 'coeffs' returns the coefficients of 'Disp' with respect to the symbolic variables 'X1' and 'X2'. When extracting coefficients of 'Disp' with 'X1' and 'X2' as variables, the equation simplifies to '-4X1^2 + 4X1X2 + X1'. This operation will return the coefficients of 'X1^2', 'X1X2' , and 'X1', which are -4, 4, and 1, respectively.

It is important to note that when obtaining coefficients with respect to 'X1', 'X1' itself cannot appear in the coefficients. This is because the operation is designed to isolate the factors multiplying 'X1' directly, not to include 'X1' as part of its own coefficient.

Refer to the following documentation to know more about 'coeffs':

https://www.mathworks.com/help/symbolic/sym.coeffs.html

Answer 2

[Star Strider]

Only request the coefficients of ‘X2’ and then divide ‘EQ_01(2)’ by ‘X1’ —

syms X1 X2 
Disp = X1*(4*X2 - 4*X1 + 1)

Disp = 

[EQ_01, T] =coeffs(Disp , X2)

EQ_01 = 

T = 

EQ_01(2) = EQ_01(2)/X1

EQ_01 = 

If you are required to get that result without the extra division by ‘X1’, be sure that you entered ‘Disp’ correctly.

.