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Groups > comp.soft-sys.math.mathematica > #1539

Re: Coefficents of terms in an expression containing the matching string

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Use proper Mathematica syntax when writing to the group.

y = 0.5*u*Exp[-2 I d1 - d2 - I d4 - phi] -
   0.5*k2*k3*u*Exp[-I d2 - I d4 - phi] -
   0.5*k2*k4*u*Exp[-I d2 - Id 3 - I phi];

List @@ y /. Exp[_] -> 1

{0.5 u, -0.5 k2 k3 u, -0.5 k2 k4 u}

If you really want to lose the signs then

List @@ y /. {Exp[_] -> 1, x_?Negative -> -x}

{0.5 u, 0.5 k2 k3 u, 0.5 k2 k4 u}

y = 0.5*u*Exp[-2 I d1 - d2 - I d4 - phi] -
   0.5*k2^2*k3*u*Exp[-I d2 - I d4 - phi] -
   0.5*k2*k4*u*Exp[-I d2 - Id 3 - I phi] -
   0.5*k2^2*k5*v*Exp[-I d2 - Id 3 - I phi];

Select[y, ! FreeQ[#, k2^2] &]

-0.5*E^((-I)*d2 - I*d4 - phi)*k2^2*k3*u - 
 0.5*E^((-I)*d2 - 3*Id - I*phi)*k2^2*k5*v


Bob Hanlon

---- Chelly <chelly85086@gmail.com> wrote: 

=============
I have two questions. The solutions may be very simple, but since I am a Mathematica novice, need some guidance.
 
1) I have an expression:
 
y = 0.5*u*exp(-2 I d1 - d2 - I d4 - phi) -
     0.5*k2*k3*u*exp(-I d2 - I d4 - phi) -
     0.5*k2*k4*u*exp(-I d2 - Id 3 - I phi) ;
 
What command should I use to get just the amplitude of each term, i.e excluding the exponential - exp(). In this case, the results needs to be
{0.5*u, 0.5*k2*k3*u, 0.5*k2*k4*u)
 
2) The second question is along similar lines. I have an expression and I need to find out the terms that have k2^2 in the amplitude
 
y = 0.5*u*exp(-2 I d1 - d2 - I d4 - phi) -
     0.5*k2^2*k3*u*exp(-I d2 - I d4 - phi) -
     0.5*k2*k4*u*exp(-I d2 - Id 3 - I phi)  -
     0.5*k2^2*k5*v*exp(-I d2 - Id 3 - I phi) ;
 
In this case, the answer is the second and last term:
0.5*k2^2*k3*u*exp(-I d2 - I d4 - phi) -
  0.5*k2^2*k5*v*exp(-I d2 - Id 3 - I phi)

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Re: Coefficents of terms in an expression containing the matching string Bob Hanlon <hanlonr@cox.net> - 2011-04-08 08:15 +0000

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