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# collecting "like terms" in an equation using symbolic toolbox

Asked by Arsalan on 19 Nov 2012

if I have a equation of such

```syms gamma vg gn Va N0 deltN Ntr eps S0 deltS taop beta B k Sinj phi0 deltPhi phi_inj
```
```equation =((gamma*vg*gn/Va)*((N0+deltN)-Ntr)/(1+eps*(S0+deltS))-1/taop)*(S0+deltS) + beta*B/Va*(N0+deltN)^2 + 2*k*sqrt(Sinj*(S0+deltS))*cos((phi0+deltPhi)-phi_inj);
```

How am I able to transform this equation using the symbolic toolbox, such that my final result will be in terms of deltS, deltN and deltPhi.

equation=collect(equation, deltS); equation=collect(equation, deltN); equation=collect(equation, deltPhi);

but I still get factors such as deltX(deltY, deltZ). but I only want a linear equation such

deltX wont be a function of either deltY or deltZ,

Thanks

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Answer by Arsalan on 21 Nov 2012

My apologizes for using the term linear equation (it should of been used there). I just want the symbolic toolbox to give me factors of such:

deltN*()+deltS()+deltPhi()

where with the factors of deltN I do not want any terms of deltS or deltPhi with the factors of deltS I do not want any terms of deltN or deltPhi with the factors of deltPhi I do not want any terms of deltS or deltN

Thanks, Arsalan

## 1 Comment

Walter Roberson on 21 Nov 2012

That isn't possible. Your first term has deltN in the numerator and deltS in the denominator. Those terms are not separable.

Answer by Walter Roberson on 19 Nov 2012

It is not possible to extract a linear equation in those variables. For example the term beta*B/Va*(N0+deltN)^2 includes deltN^2 which is non-linear.

I do not understand your reference to deltX, deltY, deltZ? Those do not appear in your equation.