# Question:Looking to collect constant terms from an expression

## Question:Looking to collect constant terms from an expression

I have a situation

`restart:with(IntegrationTools):with(PDEtools):declare(w(r));assume(delta::constant, R::constant, K:: constant, U::constant):`
`ODE_1:=diff(w(r),r)+R*(diff(w(r), r))^3-K/r;`
` `
`declare(u(r));ODE_T_1:=collect(algsubs(w(r)=u(r)+(r-1)*(U-0)/(delta-1), ODE_1),diff(u(r), r)) ;`
`eq1:=int(phi[i](r)*ODE_T_1,r=1..delta) assuming delta > 1;`
`eq2:=Expand(eq1);`
`eq3 := applyop(u->Parts(u,phi[i](r)),{3,4},eq2);`
`eq4 := [phi[i](delta)=0,phi[i](1)=0, u(1)=0, u(delta)=0];eq5 := Expand(convert(subs(eq4,eq3),diff));`
`assume(a[j]::constant):assume(a[j+1/2]::constant):assume(a[j+1]::constant):eq6:=u(r)=a[j]*phi[j](r)+a[j+1/2]*phi[j+1/2](r)+a[j+1]*phi[j+1]:eq7:=Expand(convert(subs(eq6, eq5), diff));`
` `
`This produces an output that I was expecting, but now I need to move forward and need to`
` collect terms that does not include a[j], a[j+1/2], a[j+1].`
`I have tried converting equation7 into polynomial and then try collecting terms using various`
` options but it is  not working.`
`Any suggestions??`
`Or I should have to do this manuelly??(though I dont think so, given the powerfull `
`computational engine)`
`My goal is to get system of non-linear algebraic equation for eq7 in a[j], a[j+1/2] `
`and a[j+1] by varying phi[i](r). `
`Please help.`
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