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Why does not coefficients vector include zero?

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Volkan Yangin
Volkan Yangin on 18 Jan 2021
Edited: Volkan Yangin on 18 Jan 2021
Hi,
In this code, cf should be [3 2 0], but the output is different. What is the reason of this?
Thanks,
clear all
clc
syms x y z
cf = fliplr(coeffs(x*3 + 2*y, [x y z],'All'))
>>cf =
[3, 0]
[0, 2]

Answers (1)

Bjorn Gustavsson
Bjorn Gustavsson on 18 Jan 2021
When I change the polynomial to:
cf = fliplr(coeffs(x*3 + 2*z, [x y z],'All'))
I get a 3-D array for the coefficients, as expected. What you see might be the effect of matlabs reduction of the trailing dimensions. Compare for example with:
size(randn(12,23,1))
I don't know how to solve this for you, unfortunately. Maybe you can add a term with high enough degree in your last variable to avoid that type of reduction and then crop the output for your future manipulations - this seems like a very messy idea.
HTH

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