(1) Symbolic complex algebra in mathematica and (2) Dsolve

• To: mathgroup at yoda.ncsa.uiuc.edu
• Subject: (1) Symbolic complex algebra in mathematica and (2) Dsolve
• From: ken yip <yip-ken at CS.YALE.EDU>
• Date: Thu, 22 Nov 90 18:00:16 EST

```(1) I hope I am not correct about this.  I want to define a complex quantity

z = x + I y

so that

Re[z] ==> x
Im[z] ==> y
Conjugate[z] ==> x - I y

etc.  Mathematica doesn't seem to know how to do this even after I define
x and y to be real by

x/: RealQ[x] = True

(Of course, this does not change the head of x which is still Symbol.)
Next I tried to define some transformation rules, but then I couldn't
find a way to specify the pattern variable to be of type real AND symbol.

(2) I want to solve a simple harmonic equation with boundary conditions:

DSolve[{x'[t] == y[t], y'[t] ==  k^2 x[t], y'[-h] == 0},{x[t],y[t]}, t]

But mathematica seems to ignore the boundary constraint.

Any wisdom?

P.S.  Originally I plan to use Mathematica to help me solve some
linear non-homogenous PDEs, but after a few hours playing witb it,
I am becoming increasingly frustrated with many of the simple things
it can't do.  Is that due to my insufficient knowledge of mathematica
or is that due to mathematica itself?

```

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