Collect does not do the job
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Mohammad Shojaei Arani
le 23 Nov 2021
Commenté : Mohammad Shojaei Arani
le 24 Nov 2021
Dear friends,
I have a simple question but after spending an hour I could not figur out how to fix it. So, apologies if this is a simple problem for you. As you see in bellow, I would like to write the following expression in a more compact way:
syms y y0 muY(y) dt
f=(y*diff(muY(y), y, y) - y0*diff(muY(y), y, y) + 2*muY(y)^2 + 2*diff(muY(y), y) + 2*y*muY(y)*diff(muY(y), y) - 2*y0*muY(y)*diff(muY(y), y))/dt;
More clearly, I need to re-write f in terms of (y-y0). As you see, we can do it as bellow (the command collect(f,y-y0) does not work, unfortuantely. Also, the rewrite command is limitted to soem special target functions):
f=((y-y0)*diff(muY(y), y, y) + 2*muY(y)^2 + 2*diff(muY(y), y) + 2*(y-y0)*muY(y)*diff(muY(y), y) )/dt;
which is a much nicer representation for the calculations I need to do.
Any idea?
Thanks in advance!
Babak
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Paul
le 23 Nov 2021
Here is one approach showing step-by-step. Many could be combined. Maybe there is a simpler way?
syms y y0 muY(y) dt
f=(y*diff(muY(y), y, y) - y0*diff(muY(y), y, y) + 2*muY(y)^2 + 2*diff(muY(y), y) + 2*y*muY(y)*diff(muY(y), y) - 2*y0*muY(y)*diff(muY(y), y))/dt
syms D2Y DY
f = subs(f,diff(muY,y,2),D2Y)
f =subs(f,diff(muY,y),DY)
[numf,denf] = numden(f)
syms dely
numf = subs(numf,y,dely + y0)
numf = simplify(numf)
numf = subs(numf,dely+y0,y)
numf = subs(numf,DY,diff(muY))
numf = subs(numf,D2Y,diff(muY,y,2))
numf = subs(numf,dely,y-y0)
f = numf/denf
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