So I have the following:

restart;
with(Physics):
Setup(mathematicalnotation=true,coordinatesystems=cartesian);
Define(A[mu](X));

First of all X ist defined in terms of (x,y,z,t). Is is also possible to define it in terms of (t,x,y,z) with t being mu=0.

When I do

alias(X=(t,x,y,z))

this applies only to this one vector and

d_[4] is still the time differentiation, right?

Then I wanted to construct the divergence

d_[`~mu`] A[mu](X);
TensorArray(%,performsumoverrepeatedindices=true);

This should give me sth like d1 A1 + ... + d4 A4, but it stays with d_mu A_mu ?!?

Why?

Is there also a "function" which does the contraction?

So if I have

f[mu,nu]=d_[mu] A[nu](X)

eval(f[mu,nu],nu=mu)

contract(%)

??

I want to suppress  ~ when using assume()

I write:

restart;
interface(showassumed = 0);
assume(s>0);
s;
 

but s still appears with tilde?!?

restart;

eq1 := a[n+2]+4*a[n+1]+10*a[n]-5*n-1;

applyrule(a[n::anything] = n*p+q+b[n], eq1);

eq2 := a(n+2)+4*a(n+1)+10*a(n)-5*n-1;

applyrule(a(n::anything) = b(n)+n*p+q, eq2);

eq3 := a(n+2)+4*a(n+1)+10*a(n) = 5*n+1;

applyrule(a(n::anything) = b(n)+n*p+q, eq3)

So my question is: Why does the first one not work? the second one works as expected, but the third one again does not?!

fgh := proc (x) options operator, arrow; [x, x^2, x^3] end proc;

sol := proc (x) options operator, arrow; min(`~`[Re](select(proc (t) options operator, arrow; is(abs(Im(t)) < 0.1e-19) and is(0 < Re(t)) end proc, fgh(x)))) end proc;

eval('sol(x)', [x = X]);

eval(%, X = 1)

Why does this not work?

Stupid question maybe, but when will the newest version be released or what will the newest version be label wise? When are the newest versions generally released???