Determine the coefficients in symbolic

On is dependent of In, On_1 and In_1. Is there a way to determine the coefficients multiplied on In, On_1 and In_1. On is of filetype sym.

Answer 1

[Torsten]

I don't know why the coefficients appear in the wrong order.

syms In In_1 On_1
On = 91/100*In-7/8*In_1+1/2*On_1;
coeffs(On,[In In_1 On_1])

ans = 

[Tobias Dehn Nielsen]

Thanks. I flipped the result a hope that it will work if i get anot result as well :)

[Torsten]

Note that "coeffs" only works for polynomial expressions.

[Paul]

No need to hope. Use the second output of coeffs to know whiich coefficients go with which terms:

syms In In_1 On_1
On = 91/100*In-7/8*In_1+1/2*On_1;
coeffs(On,[In In_1 On_1])

ans = 

c = coeffs(On,[In In_1 On_1])

c = 

[c,t]=coeffs(On,[In In_1 On_1])

c = 

t = 

Not sure why the single argument ouput (implict or explicit) calls return c in a different order.

[Torsten]

Looks like a bug for me.

[Paul]

I'm not sure it's a bug.

The single output form for a univariate polynomial returns coefficients from lowest to highest order

syms x
c = coeffs([2*x^2 + 3*x + 1])

c = 

But the two output form returns from highest to lowest

[c,t] = coeffs([2*x^2 + 3*x + 1])

c = 

t = 

Seems odd, but both of those cases are documented behavior.

When using the second input argument, vars, I don't see anything in the doc that says that ordering of c corresponds to the order in vars. The doc has a bunch of examples, but it doesn't really explain the process for how it orders c and t.