How to get the coefficients of a fractional polynomial from syms?

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Vinothkumar Sethurasu 2021-7-29

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回答： Paul 2021-7-29

I have a application which produces fractional polynomial as output as shown below,

syms x,
F=29.0*x*(5.7e-4*x + (5.58e-4*(0.0549*x - 0.0124*x*(0.00449*x - 1.0))*(4.92e-4*x - 1.0))/(0.00101*x - 1.0) - 1.0) - 0.141*x - (1.0*(0.0549*x - 0.0124*x*(0.00449*x - 1.0))*(4.92e-4*x - 1.0))/(0.00101*x - 1.0)

I need to know the co-efficients of the polynomial (F).

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Paul 2021-7-29

F is a rational function, i.e., the numerator and denominator are polynomials. How do you define the coefficients such a function?

Vinothkumar Sethurasu 2021-7-29

If we are going for simplification as kept, F=0

The result will be a polynomila of 'x' with order 6.

I need to find the co-efficients of that polynomial.

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Answer 1

Paul 2021-7-29

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If I correctly understand this comment (and I'm not sure I do), it sounds like you just want the coefficients of the numerator of F:

syms x

F=29.0*x*(5.7e-4*x + (5.58e-4*(0.0549*x - 0.0124*x*(0.00449*x - 1.0))*(4.92e-4*x - 1.0))/(0.00101*x - 1.0) - 1.0) - 0.141*x - (1.0*(0.0549*x - 0.0124*x*(0.00449*x - 1.0))*(4.92e-4*x - 1.0))/(0.00101*x - 1.0);

[num,den] = numden(F);

num,den

num =

den =

[coefficients,terms] = coeffs(num,'all')

coefficients =

terms =

But maybe that's still not the result you're looking for because the coeffiecients are those of a fourth order polynomial, not sixth order.